Working with data

Manipulating data using a data frame

Overview

A common lisp data frame is a collection of observations of sample variables that shares many of the properties of arrays and lists. By design it can be manipulated using the same mechanisms used to manipulate lisp arrays. This allow you to, for example, transform a data frame into an array and use array-operations to manipulate it, and then turn it into a data frame again to use in modeling or plotting.

Load/install

Data-frame is part of the Lisp-Stat package. It can be used independently if desired. Since the examples in this manual use Lisp-Stat functionality, we’ll use it from there rather than load independently.

(asdf:load-system :lisp-stat)

Within the Lisp-Stat system, the LS-USER package is the package for you to do statistics work. Type the following to enter the package:

(in-package :ls-user)

Common Lisp Implementation

Data frame is implemented as a two-dimensional common lisp data structure: a vector of vectors for data, and a hash table mapping variable names to column vectors. All columns are of equal length. This structure provides the flexibility required for column oriented manipulation, as well as speed for large data sets.

Data variables

If you’re collecting data and exploring a problem domain, you’ll sometimes have a collection of separate variable to start with. Common Lisp has two structures for holding multiple observations of variables: list and vector, collectively known as a sequence. For the most part a vector is more efficient, and the recommended way to work with variables that are independent of a data-frame.

defparameter

Lisp-Stat provides a wrapper over Common Lisp’s defparameter function to make working with data variables a little easier. You can define a variable with the def function. Here are some variables containing some weather data in Singapore over the last 14 days:

(def max-temps '#(30.1 30.3 30.3 30.8 31.6 31.5 32.7 32.1 32.1 31.4 31.9 31.7 32.2 31.1))
(def min-temps '#(24.6 25.4 25.1 24.5 23.7 25.6 24.6 24.7 25.0 25.2 25.1 25.6 25.5 25.2))
(def precipitation '#(0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.6 0.4 0.0 0.0 ))

For a quick analysis, you can see how this is easier to work with than a data-frame.

After you have been working for a while you may want to find out what variables you have defined (using def). The function variables will produce a listing:

(variables)
; => (max-temps min-temps precipitation)

If you are working with very large variables you may occasionally want to free up some space by getting rid of some variables you no longer need. You can do this using the undef function:

(undef 'max-temps)

To save a variable you can use the savevar function. This function allows you to save one or more variables into a file. A new file is created and any existing file by the same name is destroyed. To save the variable precipitation in a file called precipitation.lisp type

(savevar 'precipitation "precipitation")

Do not add the .lisp suffix yourself; savevar will supply it. To save the two variables precipitation and min-temps in the file examples.lisp type:

(savevar '(min-temps precipitation) "sg-weather")

The files precipitation.lisp and sg-weather.lisp now contain a set of expressions that, when read in with the load command, will recreate the variables precipitation and min-temp. You can look at these files with an editor like the Emacs editor and you can prepare files with your own data by following these examples.

defdf

The defdf macro is conceptually equivalent to the Common Lisp defparameter, but with some additional functionality that makes working with data frames easier. You use it the same way you’d use defparameter, for example:

(defdf foo <any-function returning a data frame> )

We’ll use both ways of defining data frames in this manual. The access methods that are defined by defdf are described in the access data section.

Create data-frames

A data frame can be created from a Common Lisp array, alist, plist or individual data vectors.

Data frame columns represent sample set variables, and its rows are observations (or cases).

(defmethod print-object ((df data-frame) stream)
  "Print the first six rows of DATA-FRAME"
  (let* ((*print-lines* 6)
	     (*print-pretty* t))
    (df:pprint-data-frame df stream nil)))
(setf *print-pretty* t)
(set-pprint-dispatch 'df:data-frame
		     #'(lambda (s df) (pprint-data-frame df s nil)))

Let’s create a simple data frame. First we’ll setup some variables to represent our sample domain:

(defparameter v #(1 2 3 4)) ; data vector
(defparameter b #*0110)     ; bits
(defparameter s #(a b c d)) ; symbols
(defparameter plist `(:vector ,v :symbols ,s))

From p/a-lists

Now, suppose we want to create a data frame from a plist

(apply #'df plist)

;; VECTOR SYMBOLS
;;      1       A
;;      2       B
;;      3       C
;;      4       D

We could also have used the plist-df function:

(plist-df plist)

;; VECTOR SYMBOLS
;;      1       A
;;      2       B
;;      3       C
;;      4       D

and to demonstrate the same thing using an alist, we’ll use the alexandria:plist-alist function to convert the plist into an alist:

(alist-df (plist-alist plist))

;; VECTOR SYMBOLS
;;      1       A
;;      2       B
;;      3       C
;;      4       D

From vectors

You can use make-df to create a data frame from keys and a list of vectors. Each vector becomes a column in the data-frame.

(make-df '(:a :b) '(#(1 2 3) #(10 20 30)))
;; A  B
;; 1 10
;; 2 20
;; 3 30

This is useful if you’ve started working with variables defined with def, defparameter or defvar and want to combine them into a data frame.

From arrays

matrix-df converts a matrix (array) to a data-frame with the given keys.

(matrix-df #(:a :b) #2A((1 2)
	                    (3 4)))
;#<DATA-FRAME (2 observations of 2 variables)>

This is useful if you need to do a lot of numeric number-crunching on a data set as an array, perhaps with BLAS or array-operations then want to add categorical variables and continue processing as a data-frame.

Example datasets

Vincent Arel-Bundock maintains a library of over 1700 R datasets that is a consolidation of example data from various R packages. You can load one of these by specifying the url to the raw data to the read-csv function. For example to load the iris data set, use:

(defdf iris
	(read-csv "https://raw.githubusercontent.com/vincentarelbundock/Rdatasets/master/csv/datasets/iris.csv")
	"Edgar Anderson's Iris Data")

Default datasets

To make the examples and tutorials easier, Lisp-Stat includes the URLs for the R built in data sets. You can see these by viewing the rdata:*r-default-datasets* variable:

LS-USER> rdata:*r-default-datasets*
(RDATA:AIRPASSENGERS RDATA:ABILITY.COV RDATA:AIRMILES RDATA:AIRQUALITY
 RDATA:ANSCOMBE RDATA:ATTENU RDATA:ATTITUDE RDATA:AUSTRES RDATA:BJSALES
 RDATA:BOD RDATA:CARS RDATA:CHICKWEIGHT RDATA:CHICKWTS RDATA:CO2-1 RDATA:CO2-2
 RDATA:CRIMTAB RDATA:DISCOVERIES RDATA:DNASE RDATA:ESOPH RDATA:EURO
 RDATA:EUSTOCKMARKETS RDATA:FAITHFUL RDATA:FORMALDEHYDE RDATA:FREENY
 RDATA:HAIREYECOLOR RDATA:HARMAN23.COR RDATA:HARMAN74.COR RDATA:INDOMETH
 RDATA:INFERT RDATA:INSECTSPRAYS RDATA:IRIS RDATA:IRIS3 RDATA:ISLANDS
 RDATA:JOHNSONJOHNSON RDATA:LAKEHURON RDATA:LH RDATA:LIFECYCLESAVINGS
 RDATA:LOBLOLLY RDATA:LONGLEY RDATA:LYNX RDATA:MORLEY RDATA:MTCARS RDATA:NHTEMP
 RDATA:NILE RDATA:NOTTEM RDATA:NPK RDATA:OCCUPATIONALSTATUS RDATA:ORANGE
 RDATA:ORCHARDSPRAYS RDATA:PLANTGROWTH RDATA:PRECIP RDATA:PRESIDENTS
 RDATA:PRESSURE RDATA:PUROMYCIN RDATA:QUAKES RDATA:RANDU RDATA:RIVERS
 RDATA:ROCK RDATA:SEATBELTS RDATA::STUDENT-SLEEP RDATA:STACKLOSS
 RDATA:SUNSPOT.MONTH RDATA:SUNSPOT.YEAR RDATA:SUNSPOTS RDATA:SWISS RDATA:THEOPH
 RDATA:TITANIC RDATA:TOOTHGROWTH RDATA:TREERING RDATA:TREES RDATA:UCBADMISSIONS
 RDATA:UKDRIVERDEATHS RDATA:UKGAS RDATA:USACCDEATHS RDATA:USARRESTS
 RDATA:USJUDGERATINGS RDATA:USPERSONALEXPENDITURE RDATA:USPOP RDATA:VADEATHS
 RDATA:VOLCANO RDATA:WARPBREAKS RDATA:WOMEN RDATA:WORLDPHONES RDATA:WWWUSAGE)

To load one of these, you can use the name of the data set. For example to load mtcars:

(defdf mtcars
  (read-csv rdata:mtcars))

If you want to load all of the default R data sets, use the rdata:load-r-default-datasets command. All the data sets included in base R will now be loaded into your environment. This is useful if you are following a R tutorial, but using Lisp-Stat for the analysis software.

You may also want to save the default R data sets in order to augment the data with labels, units, types, etc. To save all of the default R data sets to the LS:DATASETS;R directory, use the (rdata:save-r-default-datasets) command if the default data sets have already been loaded, or save-r-data if they have not. This saves the data in lisp format.

All datasets

To work with all of the R data sets, we recommend you use git to download the repository to your hard drive. For example I downloaded the example data to the s: drive like this:

cd s:
git clone https://github.com/vincentarelbundock/Rdatasets.git

and setup a logical host in my ls-init.lisp file like so:

;;; Define logical hosts for external data sets
(setf (logical-pathname-translations "RDATA")
	`(("**;*.*.*" ,(merge-pathnames "csv/**/*.*" "s:/Rdatasets/"))))

Now you can access any of the datasets using the logical pathname. Here’s an example of creating a data frame using the ggplot mpg data set:

(defdf mpg (read-csv #P"RDATA:ggplot2;mpg.csv"))

Searching the examples

With so many data sets, it’s helpful to load the index into a data frame so you can search for specific examples. You can do this by loading the rdata:index into a data frame:

(defdf rindex (read-csv rdata:index))

I find it easiest to use the SQL-DF system to query this data. For example if you wanted to find the data sets with the largest number of observations:

(pprint-data-frame
	(sqldf "select item, title, rows, cols from rindex order by rows desc limit 10"))

;;   ITEM            TITLE                                                               ROWS COLS
;; 0 military        US Military Demographics                                         1414593    6
;; 1 Birthdays       US Births in 1969 - 1988                                          372864    7
;; 2 wvs_justifbribe Attitudes about the Justifiability of Bribe-Taking in the ...     348532    6
;; 3 flights         Flights data                                                      336776   19
;; 4 wvs_immig       Attitudes about Immigration in the World Values Survey            310388    6
;; 5 Fertility       Fertility and Women's Labor Supply                                254654    8
;; 6 avandia         Cardiovascular problems for two types of Diabetes medicines       227571    2
;; 7 AthleteGrad     Athletic Participation, Race, and Graduation                      214555    3
;; 8 mortgages       Data from "How do Mortgage Subsidies Affect Home Ownership? ..."  214144    6
;; 9 mammogram       Experiment with Mammogram Randomized

Export data frames

These next few functions are the reverse of the ones above used to create them. These are useful when you want to use foreign libraries or common lisp functions to process the data.

For this section of the manual, we are going to work with a subset of the mtcars data set from above. We’ll use the select package to take the first 5 rows so that the data transformations are easier to see.

(defparameter mtcars-small (select mtcars (range 0 5) t))

The next three functions convert a data-frame to and from standard common lisp data structures. This is useful if you’ve got data in Common Lisp format and want to work with it in a data frame, or if you’ve got a data frame and want to apply Common Lisp operators on it that don’t exist in df.

as-alist

Just like it says on the tin, as-alist takes a data frame and returns an alist version of it (formatted here for clearer output – a pretty printer that outputs an alist in this format would be a welcome addition to Lisp-Stat)

(as-alist mtcars-small)
;; ((MTCARS:X1 . #("Mazda RX4" "Mazda RX4 Wag" "Datsun 710" "Hornet 4 Drive" "Hornet Sportabout"))
;;  (MTCARS:MPG . #(21 21 22.8d0 21.4d0 18.7d0))
;;  (MTCARS:CYL . #(6 6 4 6 8))
;;  (MTCARS:DISP . #(160 160 108 258 360))
;;  (MTCARS:HP . #(110 110 93 110 175))
;;  (MTCARS:DRAT . #(3.9d0 3.9d0 3.85d0 3.08d0 3.15d0))
;;  (MTCARS:WT . #(2.62d0 2.875d0 2.32d0 3.215d0 3.44d0))
;;  (MTCARS:QSEC . #(16.46d0 17.02d0 18.61d0 19.44d0 17.02d0))
;;  (MTCARS:VS . #*00110)
;;  (MTCARS:AM . #*11100)
;;  (MTCARS:GEAR . #(4 4 4 3 3))
;;  (MTCARS:CARB . #(4 4 1 1 2)))

as-plist

Similarly, as-plist will return a plist:

(as-plist mtcars-small)
;; (MTCARS:X1 #("Mazda RX4" "Mazda RX4 Wag" "Datsun 710" "Hornet 4 Drive" "Hornet Sportabout")
;;  MTCARS:MPG #(21 21 22.8d0 21.4d0 18.7d0)
;;	MTCARS:CYL #(6 6 4 6 8)
;;	MTCARS:DISP #(160 160 108 258 360)
;;	MTCARS:HP #(110 110 93 110 175)
;;	MTCARS:DRAT #(3.9d0 3.9d0 3.85d0 3.08d0 3.15d0)
;;	MTCARS:WT #(2.62d0 2.875d0 2.32d0 3.215d0 3.44d0)
;;	MTCARS:QSEC #(16.46d0 17.02d0 18.61d0 19.44d0 17.02d0)
;;	MTCARS:VS #*00110
;;	MTCARS:AM #*11100
;;	MTCARS:GEAR #(4 4 4 3 3)
;;	MTCARS:CARB #(4 4 1 1 2))

as-array

as-array returns the data frame as a row-major two dimensional lisp array. You’ll want to save the variable names using the keys function to make it easy to convert back (see matrix-df). One of the reasons you might want to use this function is to manipulate the data-frame using array-operations. This is particularly useful when you have data frames of all numeric values.

(defparameter mtcars-keys (keys mtcars)) ; we'll use later
(defparameter mtcars-small-array (as-array mtcars-small))
mtcars-small-array
;; 0 Mazda RX4         21.0 6 160 110 3.90 2.620 16.46 0 1 4 4
;; 1 Mazda RX4 Wag     21.0 6 160 110 3.90 2.875 17.02 0 1 4 4
;; 2 Datsun 710        22.8 4 108  93 3.85 2.320 18.61 1 1 4 1
;; 3 Hornet 4 Drive    21.4 6 258 110 3.08 3.215 19.44 1 0 3 1
;; 4 Hornet Sportabout 18.7 8 360 175 3.15 3.440 17.02 0 0 3 2

Our abbreviated mtcars data frame is now a two dimensional Common Lisp array. It may not look like one because Lisp-Stat will ‘print pretty’ arrays. You can inspect it with the describe command to make sure:

LS-USER> (describe mtcars-small-array)
...

Type: (SIMPLE-ARRAY T (5 12))
Class: #<BUILT-IN-CLASS SIMPLE-ARRAY>
Element type: T
Rank: 2
Physical size: 60

vectors

The columns function returns the variables of the data frame as a vector of vectors:

(columns mtcars-small)
; #(#("Mazda RX4" "Mazda RX4 Wag" "Datsun 710" "Hornet 4 Drive" "Hornet Sportabout")
;   #(21 21 22.8d0 21.4d0 18.7d0)
;	#(6 6 4 6 8)
;	#(160 160 108 258 360)
;	#(110 110 93 110 175)
;	#(3.9d0 3.9d0 3.85d0 3.08d0 3.15d0)
;	#(2.62d0 2.875d0 2.32d0 3.215d0 3.44d0)
;	#(16.46d0 17.02d0 18.61d0 19.44d0 17.02d0)
;	#*00110
;	#*11100
;	#(4 4 4 3 3)
;	#(4 4 1 1 2))

This is a column-major lisp array.

You can also pass a selection to the columns function to return specific columns:

(columns mtcars-small 'mtcars:mpg)
; #(21 21 22.8d0 21.4d0 18.7d0)

The functions in array-operations are helpful in further dealing with data frames as vectors and arrays. For example you could convert a data frame to a transposed array by using aops:combine with the columns function:

(combine (columns mtcars-small))
;;  0 Mazda RX4 Mazda RX4 Wag Datsun 710 Hornet 4 Drive Hornet Sportabout
;;  1     21.00        21.000      22.80         21.400             18.70
;;  2      6.00         6.000       4.00          6.000              8.00
;;  3    160.00       160.000     108.00        258.000            360.00
;;  4    110.00       110.000      93.00        110.000            175.00
;;  5      3.90         3.900       3.85          3.080              3.15
;;  6      2.62         2.875       2.32          3.215              3.44
;;  7     16.46        17.020      18.61         19.440             17.02
;;  8      0.00         0.000       1.00          1.000              0.00
;;  9      1.00         1.000       1.00          0.000              0.00
;; 10      4.00         4.000       4.00          3.000              3.00
;; 11      4.00         4.000       1.00          1.000              2.00

Load data

You can use the dfio system to load delimited text files, such as CSV, into a data frame.

From strings

Here is a short demonstration of reading from strings:

(defparameter *d*
  (read-csv
   (format nil "Gender,Age,Height~@
              \"Male\",30,180.~@
              \"Male\",31,182.7~@
               \"Female\",32,1.65e2")))

dfio tries to hard to decipher the various number formats sometimes encountered in CSV files:

(select (dfio:read-csv
                 (format nil "\"All kinds of wacky number formats\"~%.7~%19.~%.7f2"))
                t 'all-kinds-of-wacky-number-formats)
; => #(0.7d0 19.0d0 70.0)

From files

We saw above that dfio can read from strings, so one easy way to read from a file is to use the uiop system function read-file-string. We can read one of the example data files included with Lisp-Stat like this:

(read-csv
	(uiop:read-file-string #P"LS:DATASETS;absorbtion.csv"))
;;    IRON ALUMINUM ABSORPTION 
;;  0   61       13          4
;;  1  175       21         18
;;  2  111       24         14
;;  3  124       23         18
;;  4  130       64         26
;;  5  173       38         26 ..

For most data sets, this method will work fine. If you are working with large CSV files, you may want to consider using a stream from an open file so you don’t have uiop read the whole thing in before processing it into a data frame:

(read-csv #P"LS:DATASETS;absorbtion.csv")
;;    IRON ALUMINUM ABSORPTION
;;  0   61       13          4
;;  1  175       21         18
;;  2  111       24         14
;;  3  124       23         18
;;  4  130       64         26
;;  5  173       38         26 ..

From URLs

dfio can also read from Common Lisp streams. Streams operations can be network or file based. Here is an example of how to read the classic Iris data set over the network:

(read-csv
   "https://raw.githubusercontent.com/vincentarelbundock/Rdatasets/master/csv/datasets/iris.csv")

;;     X27 SEPAL-LENGTH SEPAL-WIDTH PETAL-LENGTH PETAL-WIDTH SPECIES
;;   0   1          5.1         3.5          1.4         0.2 setosa
;;   1   2          4.9         3.0          1.4         0.2 setosa
;;   2   3          4.7         3.2          1.3         0.2 setosa
;;   3   4          4.6         3.1          1.5         0.2 setosa
;;   4   5          5.0         3.6          1.4         0.2 setosa
;;   5   6          5.4         3.9          1.7         0.4 setosa ..

From a database

You can load data from a SQLite table using the read-table command. Here’s an example of reading the iris data frame from a SQLite table:

(asdf:load-system :sqldf)
(defdf iris
	(sqldf:read-table
		(sqlite:connect #P"S:\\src\\lisp-stat\\datasets\\iris.db3")
		"iris"))

Note that sqlite:connect does not take a logical pathname; use a system path appropriate for your computer. One reason you might want to do this is for speed in loading CSV. The CSV loader for SQLite is 10-15 times faster than the fastest Common Lisp CSV parser, and it is often quicker to load to SQLite first, then load into Lisp.

Save data

Data frames can be saved into any delimited text format supported by fare-csv, or several flavors of JSON, such as Vega-Lite. Since the JSON reader/writers are specific to the plotting applications, they are described in the plotting section.

As CSV

To save the mtcars data frame to disk, you could use:

(write-csv mtcars
		   #P"LS:DATASETS;mtcars.csv"
           :add-first-row t)         ; add column headers

to save it as CSV, or to save it to tab-separated values:

(write-csv mtcars
	       #P"LS:DATASETS;mtcars.tsv"
	       :separator #\tab
		   :add-first-row t)         ; add column headers

As Lisp

For the most part, you will want to save your data frames as lisp. Doing so is both faster in loading, but more importantly it preserves any variable attributes that may have been given.

To save a data frame, use the save command:

(save 'mtcars #P"LS:DATASETS;mtcars.lisp")

Note that in this case you are passing the symbol to the function, not the value (thus the quote (') before the name of the data frame).

To a database

The write-table function can be used to save a data frame to a SQLite database. Each take a connection to a database, which may be file or memory based, a table name and a data frame. Multiple data frames, with different table names, may be written to a single SQLite file this way.

Access data

This section describes various way to access data variables.

Access a data-frame

Let’s use defdf to define the iris data frame. We’ll use both of these data frames in the examples below.

(defdf iris
  (read-csv rdata:iris))
COMMON-LISP:WARNING: Missing column name was filled in
"IRIS"

We now have a global variable named iris that represents the data frame. Let’s look at the first part of this data:

(head iris)
;;   X29 SEPAL-LENGTH SEPAL-WIDTH PETAL-LENGTH PETAL-WIDTH SPECIES
;; 0   1          5.1         3.5          1.4         0.2 setosa
;; 1   2          4.9         3.0          1.4         0.2 setosa
;; 2   3          4.7         3.2          1.3         0.2 setosa
;; 3   4          4.6         3.1          1.5         0.2 setosa
;; 4   5          5.0         3.6          1.4         0.2 setosa
;; 5   6          5.4         3.9          1.7         0.4 setosa

Notice a couple of things. First, there is a column X29. In fact if you look back at previous data frame output in this tutorial you will notice various columns named X followed by some number. This is because the column was not given a name in the data set, so a name was generated for it. X starts at 1 and increased by 1 each time an unnamed variable is encountered during your Lisp-Stat session. The next time you start Lisp-Stat, numbering will begin from 1 again. We will see how to clean this up this data frame in the next sections.

The second thing to note is the row numbers on the far left side. When Lisp-Stat prints a data frame it automatically adds row numbers. Row and column numbering in Lisp-Stat start at 0. In R they start with 1. Row numbers make it convenient to select data sections from a data frame, but they are not part of the data and cannot be selected or manipulated themselves. They only appear when a data frame is printed.

Access a variable

The defdf macro also defines symbol macros that allow you to refer to a variable by name, for example to refer to the mpg column of mtcars, you can refer to it by the the name data-frame:variable convention.

mtcars:mpg
; #(21 21 22.8D0 21.4D0 18.7D0 18.1D0 14.3D0 24.4D0 22.8D0 19.2D0 17.8D0 16.4D0
  17.3D0 15.2D0 10.4D0 10.4D0 14.7D0 32.4D0 30.4D0 33.9D0 21.5D0 15.5D0 15.2D0
  13.3D0 19.2D0 27.3D0 26 30.4D0 15.8D0 19.7D0 15 21.4D0)

There is a point of distinction to be made here: the values of mpg and the column mpg. For example to obtain the same vector using the selection/sub-setting package select we must refer to the column:

(select mtcars t 'mpg)
; #(21 21 22.8D0 21.4D0 18.7D0 18.1D0 14.3D0 24.4D0 22.8D0 19.2D0 17.8D0 16.4D0
  17.3D0 15.2D0 10.4D0 10.4D0 14.7D0 32.4D0 30.4D0 33.9D0 21.5D0 15.5D0 15.2D0
  13.3D0 19.2D0 27.3D0 26 30.4D0 15.8D0 19.7D0 15 21.4D0)

Note that with select we passed the symbol ‘mpg (you can tell it’s a symbol because of the quote in front of it).

So, the rule here is, if you want the value, refer to it directly, e.g. mtcars:mpg. If you are referring to the column, use the symbol. Data frame operations typically require the symbol, where as Common Lisp and other packages that take vectors use the direct access form.

Data-frame operations

These functions operate on data-frames as a whole.

copy

copy returns a newly allocated data-frame with the same values as the original:

(copy mtcars-small)
;;   X1                 MPG CYL DISP  HP DRAT    WT  QSEC VS AM GEAR CARB
;; 0 Mazda RX4         21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
;; 1 Mazda RX4 Wag     21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
;; 2 Datsun 710        22.8   4  108  93 3.85 2.320 18.61  1  1    4    1
;; 3 Hornet 4 Drive    21.4   6  258 110 3.08 3.215 19.44  1  0    3    1
;; 4 Hornet Sportabout 18.7   8  360 175 3.15 3.440 17.02  0  0    3    2

By default only the keys are copied and the original data remains the same, i.e. a shallow copy. For a deep copy, use the copy-array function as the key:

(copy mtcars-small :key #'copy-array)
;;   X1                 MPG CYL DISP  HP DRAT    WT  QSEC VS AM GEAR CARB
;; 0 Mazda RX4         21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
;; 1 Mazda RX4 Wag     21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
;; 2 Datsun 710        22.8   4  108  93 3.85 2.320 18.61  1  1    4    1
;; 3 Hornet 4 Drive    21.4   6  258 110 3.08 3.215 19.44  1  0    3    1
;; 4 Hornet Sportabout 18.7   8  360 175 3.15 3.440 17.02  0  0    3    2

Useful when applying destructive operations to the data-frame.

keys

Returns a vector of the variables in the data frame. The keys are symbols. Symbol properties describe the variable, for example units.

(keys mtcars)
; #(X45 MPG CYL DISP HP DRAT WT QSEC VS AM GEAR CARB)

Recall the earlier discussion of X1 for the column name.

map-df

map-df transforms one data-frame into another, row-by-row. Its function signature is:

(map-df data-frame keys function result-keys) ...

It applies function to each row, and returns a data frame with the result-keys as the column (variable) names. keys is a list. You can also specify the type of the new variables in the result-keys list.

The goal for this example is to transform df1:

(defparameter df1 (make-df '(:a :b) '(#(2 3 5) #(7 11 13))))

into a data-frame that consists of the product of :a and :b, and a bit mask of the columns that indicate where the value is <= 30. First we’ll need a helper for the bit mask:

(defun predicate-bit (a b)
  "Return 1 if a*b <= 30, 0 otherwise"
  (if (<= 30 (* a b))
      1
      0))

Now we can transform df1 into our new data-frame, df2, with:

(defparameter df2 (map-df df1 '(:a :b)
			  (lambda (a b)
			    (vector (* a b) (predicate-bit a b)))
			  '((:p fixnum) (:m bit))))

Since it was a parameter assignment, we have to view it manually:

(pprint df2)
;;    P M
;; 0 14 0
;; 1 33 1
;; 2 65 1

Note how we specified both the new key names and their type. Here’s an example that transforms the units of mtcars from imperial to metric:

(map-df mtcars '(x1 mpg disp hp wt)
	(lambda (model mpg disp hp wt)
	  (vector model ;no transformation for model (X1), return as-is
              (/ 235.214583 mpg)
		      (/ disp 61.024)
		      (* hp 1.01387)
		      (/ (* wt 1000) 2.2046)))
	'(:model (:100km/l float) (:disp float) (:hp float) (:kg float)))

;;    MODEL                 100KM/L    DISP        HP         KG
;;  0 Mazda RX4             11.2007  2.6219  111.5257  1188.4242
;;  1 Mazda RX4 Wag         11.2007  2.6219  111.5257  1304.0914
;;  2 Datsun 710            10.3164  1.7698   94.2899  1052.3451
;;  3 Hornet 4 Drive        10.9913  4.2278  111.5257  1458.3144
;;  4 Hornet Sportabout     12.5783  5.8993  177.4272  1560.3737
;;  5 Valiant               12.9953  3.6871  106.4564  1569.4456
;;  6 Duster 360            16.4486  5.8993  248.3981  1619.3413
;;  7 Merc 240D              9.6399  2.4040   62.8599  1446.9744
;;  8 Merc 230              10.3164  2.3073   96.3176  1428.8306
;;  9 Merc 280              12.2508  2.7465  124.7060  1560.3737
;; 10 Merc 280C             13.2143  2.7465  124.7060  1560.3737
;; 11 Merc 450SE            14.3424  4.5195  182.4966  1846.1398
;; 12 Merc 450SL            13.5962  4.5195  182.4966  1691.9168
;; 13 Merc 450SLC           15.4746  4.5195  182.4966  1714.5967
;; 14 Cadillac Fleetwood    22.6168  7.7347  207.8434  2381.3843
;; 15 Lincoln Continental   22.6168  7.5380  217.9821  2460.3102
;; 16 Chrysler Imperial     16.0010  7.2103  233.1901  2424.4760
;; 17 Fiat 128               7.2597  1.2897   66.9154   997.9134
;; 18 Honda Civic            7.7373  1.2405   52.7212   732.5592
;; 19 Toyota Corolla         6.9385  1.1651   65.9016   832.3505
;; 20 Toyota Corona         10.9402  1.9681   98.3454  1118.1166
;; 21 Dodge Challenger      15.1751  5.2111  152.0805  1596.6615
;; 22 AMC Javelin           15.4746  4.9816  152.0805  1558.1057 ..

Note that you may have to adjust the X column name to suit your current environment.

You might be wondering how we were able to refer to the columns without the ' (quote); in fact we did, at the beginning of the list. The lisp reader then reads the contents of the list as symbols.

print

The pprint command will print a data frame in a nicely formatted way, respecting the pretty printing row/column length variables:

(pprint mtcars)
;; MODEL                MPG CYL  DISP  HP DRAT    WT  QSEC VS AM GEAR CARB
;; Mazda RX4           21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
;; Mazda RX4 Wag       21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
;; Datsun 710          22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1
;; Hornet 4 Drive      21.4   6 258.0 110 3.08 3.215 19.44  1  0    3    1
...
;; Output elided for brevity

rows

rows returns the rows of a data frame as a vector of vectors:

(rows mtcars-small)
;#(#("Mazda RX4" 21 6 160 110 3.9d0 2.62d0 16.46d0 0 1 4 4)
;  #("Mazda RX4 Wag" 21 6 160 110 3.9d0 2.875d0 17.02d0 0 1 4 4)
;  #("Datsun 710" 22.8d0 4 108 93 3.85d0 2.32d0 18.61d0 1 1 4 1)
;  #("Hornet 4 Drive" 21.4d0 6 258 110 3.08d0 3.215d0 19.44d0 1 0 3 1)
;  #("Hornet Sportabout" 18.7d0 8 360 175 3.15d0 3.44d0 17.02d0 0 0 3 2))

remove duplicates

The df-remove-duplicates function will remove duplicate rows. Let’s create a data-frame with duplicates:

(defparameter dup (make-df '(a b c) '(#(a1 a1 a3)
                                      #(a1 a1 b3)
									  #(a1 a1 c3))))
DUP

;;    A  B  C
;; 0 A1 A1 A1
;; 1 A1 A1 A1
;; 2 A3 B3 C3

Now remove duplicate rows 0 and 1:

(df-remove-duplicates dup)
;; A  B  C
;; A1 A1 A1
;; A3 B3 C3

remove dataframe

If you are working with large data sets, you may wish to remove a data frame from your environment to save memory. The undef command does this:

LS-USER> (undef 'toothgrowth)
TOOTHGROWTH

You can check that it was removed with the show-data-frames function.

show

To list the data frames in your environment, use the show-data-frames function. Here is an example of what is currently loaded into the authors environment. The data frames listed may be different for you, depending on what you have loaded.

LS-USER> (show-data-frames)
#<DATA-FRAME AQ (153 observations of 7 variables)>

#<DATA-FRAME MTCARS (32 observations of 12 variables)
Motor Trend Car Road Tests>

#<DATA-FRAME USARRESTS (50 observations of 5 variables)
Violent Crime Rates by US State>

#<DATA-FRAME PLANTGROWTH (30 observations of 3 variables)
Results from an Experiment on Plant Growth>

#<DATA-FRAME TOOTHGROWTH (60 observations of 4 variables)
The Effect of Vitamin C on Tooth Growth in Guinea Pigs>

with the :head t option, show-data-frames will print the first five rows of the data frame, similar to the head command:

LS-USER> (show-data-frames :head t)
AQ
;;  X5             OZONE SOLAR-R WIND TEMP MONTH DAY
;;   1           41.0000     190  7.4   67     5   1
;;   2           36.0000     118  8.0   72     5   2
;;   3           12.0000     149 12.6   74     5   3
;;   4           18.0000     313 11.5   62     5   4
;;   5           42.1293      NA 14.3   56     5   5
;;   6           28.0000      NA 14.9   66     5   6 ..

MTCARS
;; MODEL                MPG CYL  DISP  HP DRAT    WT  QSEC VS AM GEAR CARB
;; Mazda RX4           21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
;; Mazda RX4 Wag       21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
;; Datsun 710          22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1
;; Hornet 4 Drive      21.4   6 258.0 110 3.08 3.215 19.44  1  0    3    1
;; Hornet Sportabout   18.7   8 360.0 175 3.15 3.440 17.02  0  0    3    2
;; Valiant             18.1   6 225.0 105 2.76 3.460 20.22  1  0    3    1 ..

;; Output elided for brevity

Column operations

You have seen some of these functions before, and for completeness we repeat them here.

To obtain a variable (column) from a data frame, use the column function. Using the mtcars-small data frame, defined in export data frames above:

(column mtcars-small 'mtcars:mpg)
;; #(21 21 22.8d0 21.4d0 18.7d0)

To get all the columns as a vector, use the columns function:

(columns mtcars-small)
; #(#("Mazda RX4" "Mazda RX4 Wag" "Datsun 710" "Hornet 4 Drive" "Hornet Sportabout")
;   #(21 21 22.8d0 21.4d0 18.7d0)
;	#(6 6 4 6 8)
;	#(160 160 108 258 360)
;	#(110 110 93 110 175)
;	#(3.9d0 3.9d0 3.85d0 3.08d0 3.15d0)
;	#(2.62d0 2.875d0 2.32d0 3.215d0 3.44d0)
;	#(16.46d0 17.02d0 18.61d0 19.44d0 17.02d0)
;	#*00110
;	#*11100
;	#(4 4 4 3 3)
;	#(4 4 1 1 2))

You can also return a subset of the columns by passing in a selection:

(columns mtcars-small '(mtcars:mpg mtcars:wt))
;; #(#(21 21 22.8d0 21.4d0 18.7d0) #(2.62d0 2.875d0 2.32d0 3.215d0 3.44d0))

Add columns

There are two ‘flavors’ of add functions, destructive and non-destructive. The latter return a new data frame as the result, and the destructive versions modify the data frame passed as a parameter. The destructive versions are denoted with a ‘!’ at the end of the function name.

To add a single column to a data frame, use the add-column! function. We’ll use a data frame similar to the one used in our reading data-frames from a string example to illustrate column operations

(defparameter *d* (read-csv
		   (format nil "Gender,Age,Height
                              \"Male\",30,180
                              \"Male\",31,182
                              \"Female\",32,165
	                          \"Male\",22,167
	                          \"Female\",45,170")))
(pprint *d*)
;;   GENDER AGE HEIGHT
;; 0 Male    30    180
;; 1 Male    31    182
;; 2 Female  32    165
;; 3 Male    22    167
;; 4 Female  45    170

and add a ‘weight’ column to it:

(add-column! *d* 'weight #(75.2 88.5 49.4 78.1 79.4))

;;   GENDER AGE HEIGHT WEIGHT
;; 0 Male    30    180   75.2
;; 1 Male    31    182   88.5
;; 2 Female  32    165   49.4
;; 3 Male    22    167   78.1
;; 4 Female  45    170   79.4

now that we have weight, let’s add a BMI column to it to demonstrate using a function to compute the new column values:

(add-column! *d* 'bmi
	     (map-rows *d* '(height weight)
		       #'(lambda (h w) (/ w (square (/ h 100))))))
;;   SEX    AGE HEIGHT WEIGHT       BMI
;; 0 Female  10    180   75.2 23.209875
;; 1 Female  15    182   88.5 26.717787
;; 2 Male    20    165   49.4 18.145086
;; 3 Female  25    167   78.1 28.003874
;; 4 Male    30    170   79.4 27.474049

Now let’s add multiple columns destructively using add-columns!

(add-columns! *d* 'a #(1 2 3 4 5) 'b #(foo bar baz qux quux))

;; GENDER AGE HEIGHT WEIGHT       BMI A    B
;; Male    30    180   75.2   23.2099 1  FOO
;; Male    31    182   88.5   26.7178 2  BAR
;; Female  32    165   49.4   18.1451 3  BAZ
;; Male    22    167   78.1   28.0039 4  QUX
;; Female  45    170   79.4   27.4740 5 QUUX

Add properties

As part of the recoding and data cleansing process, you will want to add properties to your variables. In Common Lisp, these are plists that reside on the variable symbols, e.g. mtcars:mpg. In R they are known as attributes. By default, there are three properties for each variable: type, unit and label (documentation). When you load from external formats, like CSV, these properties are all nil; when you load from a lisp file, they will have been saved along with the data (if you set them).

type

It is important to note that there are two ‘types’ in Lisp-Stat: the implementation type and the ‘statistical’ type. Sometimes these are the same, such as in the case of reals; in other situations they are not. A good example of this can be seen in the mtcars data set. The hp (horsepower), gear and carb are all of type integer from an implementation perspective. However only horsepower is a continuous variable. You can have an additional 0.5 horsepower, but you cannot add an additional 0.5 gears or carburetors.

Most of the time the heuristics in the summary function try to do the ‘right thing’ when printing summaries and you won’t notice the difference. You will need to use the describe function to see the details of the type property.

A typical case, seen in mtcars, is a variable to be of type float, but a few entries will be entered as integers. The values may be equivalent, but the types are not. The CSV loader has no way of knowing, so loads the column as a mixture of integers and floats. Let’s reload mtcars from the CSV and work through some examples.

(undef 'mtcars)
(defdf mtcars (read-csv rdata:mtcars))

and look at the mpg variable:

LS-USER> mtcars:mpg
#(21 21 22.8d0 21.4d0 18.7d0 18.1d0 14.3d0 24.4d0 22.8d0 19.2d0 17.8d0 16.4d0
  17.3d0 15.2d0 10.4d0 10.4d0 14.7d0 32.4d0 30.4d0 33.9d0 21.5d0 15.5d0 15.2d0
  13.3d0 19.2d0 27.3d0 26 30.4d0 15.8d0 19.7d0 15 21.4d0)
LS-USER> (type-of *)
(SIMPLE-VECTOR 32)

Notice that the first two entries in the vector are integers, and the remainder floats. To fix this manually, you will need to coerce each element of the column to type double-float and then change the type of the vector to a specialised float vector.

You can use heuristicate-types function to guess the statistical types for you. For reals and strings, heuristicate-types works fine, however because integers are used to both encode factors as well as numeric values, you will have to indicate the type using set-properties. We see this below with gear and carb, although implemented as integer, they are actually type factor. The next section describes how to set them.

Using describe, we can view the types of all the variables that heuristicate-types set:

LS-USER> (heuristicate-types mtcars)
LS-USER> (describe mtcars)
MTCARS
  A data-frame with 32 observations of 12 variables

Variable | Type         | Unit | Label
-------- | ----         | ---- | -----------
X8       | STRING       | NIL  | NIL
MPG      | DOUBLE-FLOAT | NIL  | NIL
CYL      | INTEGER      | NIL  | NIL
DISP     | DOUBLE-FLOAT | NIL  | NIL
HP       | INTEGER      | NIL  | NIL
DRAT     | DOUBLE-FLOAT | NIL  | NIL
WT       | DOUBLE-FLOAT | NIL  | NIL
QSEC     | DOUBLE-FLOAT | NIL  | NIL
VS       | BIT          | NIL  | NIL
AM       | BIT          | NIL  | NIL
GEAR     | INTEGER      | NIL  | NIL
CARB     | INTEGER      | NIL  | NIL

unit & labels

To add units or labels to the data frame, use the set-properties function. This function takes an alist of variable/value pairs, so to set the units and labels:

(set-properties mtcars :unit '(:mpg m/g
			       :cyl :NA
			       :disp in³
			       :hp hp
			       :drat :NA
			       :wt lb
			       :qsec s
			       :vs :NA
			       :am :NA
			       :gear :NA
			       :carb :NA))

(set-properties mtcars :label '(:mpg "Miles/(US) gallon"
				:cyl "Number of cylinders"
				:disp "Displacement (cu.in.)"
				:hp "Gross horsepower"
				:drat "Rear axle ratio"
				:wt "Weight (1000 lbs)"
				:qsec "1/4 mile time"
				:vs "Engine (0=v-shaped, 1=straight)"
				:am "Transmission (0=automatic, 1=manual)"
				:gear "Number of forward gears"
				:carb "Number of carburetors"))

Now look at the description again:

LS-USER> (describe mtcars)
MTCARS
  A data-frame with 32 observations of 12 variables

Variable | Type         | Unit | Label
-------- | ----         | ---- | -----------
X8       | STRING       | NIL  | NIL
MPG      | DOUBLE-FLOAT | M/G  | Miles/(US) gallon
CYL      | INTEGER      | NA   | Number of cylinders
DISP     | DOUBLE-FLOAT | IN3  | Displacement (cu.in.)
HP       | INTEGER      | HP   | Gross horsepower
DRAT     | DOUBLE-FLOAT | NA   | Rear axle ratio
WT       | DOUBLE-FLOAT | LB   | Weight (1000 lbs)
QSEC     | DOUBLE-FLOAT | S    | 1/4 mile time
VS       | BIT          | NA   | Engine (0=v-shaped, 1=straight)
AM       | BIT          | NA   | Transmission (0=automatic, 1=manual)
GEAR     | INTEGER      | NA   | Number of forward gears
CARB     | INTEGER      | NA   | Number of carburetors

You can set any properties you like with this command. To make your custom properties appear in the describe command and be saved automatically, override the describe and write-df methods, or use :after methods.

Finally, to set the type for gear and carb properly, we can use:

(set-properties mtcars :type '(:gear :factor :carb :factor))

Note: The value for the property here is :factor, a keyword. This signifies that it is not an implementation type, but a statistical type.

Now we have the data frame in its final form:

LS-USER> (describe mtcars)

Variable | Type         | Unit | Label
-------- | ----         | ---- | -----------
MODEL    | STRING       | NIL  | NIL
MPG      | DOUBLE-FLOAT | M/G  | Miles/(US) gallon
CYL      | INTEGER      | NA   | Number of cylinders
DISP     | DOUBLE-FLOAT | IN3  | Displacement (cu.in.)
HP       | INTEGER      | HP   | Gross horsepower
DRAT     | DOUBLE-FLOAT | NA   | Rear axle ratio
WT       | DOUBLE-FLOAT | LB   | Weight (1000 lbs)
QSEC     | DOUBLE-FLOAT | S    | 1/4 mile time
VS       | BIT          | NA   | Engine (0=v-shaped, 1=straight)
AM       | BIT          | NA   | Transmission (0=automatic, 1=manual)
GEAR     | FACTOR       | NA   | Number of forward gears
CARB     | FACTOR       | NA   | Number of carburetors

A final note: string variables are not encoded as factors automatically. This is different than earlier version of R. R’s behaviour in version 4.0 and onward is the same as Lisp-Stat.

Remove columns

Let’s remove the columns a and b that we just added above with the remove-columns function. Since it returns a new data frame, we’ll need to assign the return value to *d*:

(setf *d* (remove-columns *d* '(a b bmi)))

;; GENDER AGE HEIGHT WEIGHT       BMI
;; Male    30    180   75.2   23.2099
;; Male    31    182   88.5   26.7178
;; Female  32    165   49.4   18.1451
;; Male    22    167   78.1   28.0039
;; Female  45    170   79.4   27.4740

Rename columns

Sometimes data sources can have variable names that we want to change. To do this, use the substitute-key! function. This example will rename the ‘gender’ variable to ‘sex’:

(substitute-key! *d* 'sex 'gender)
; => #<ORDERED-KEYS WEIGHT, HEIGHT, AGE, SEX>

If you used defdf to create your data frame, and this is the recommended way, then use the replace-key! macro to rename the column and update the variable references within the data package. Let’s use this now to rename the mtcars X1 variable to model. First a quick look at the first 2 rows as they are now:

(head mtcars 2)
;;   X1                 MPG CYL DISP  HP DRAT    WT  QSEC VS AM GEAR CARB
;; 0 Mazda RX4         21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
;; 1 Mazda RX4 Wag     21.0   6  160 110 3.90 2.875 17.02  0  1    4    4

Replace X1 with model:

(replace-key! mtcars model x1)

Note: check to see what value your version of mtcars has. In this case, with a fresh start of Lisp-Stat, it has X1. It could have X2, X3, etc.

Now check that it worked:

(head mtcars 2)
;;   MODEL         MPG CYL DISP  HP DRAT    WT  QSEC VS AM GEAR CARB
;; 0 Mazda RX4      21   6  160 110  3.9 2.620 16.46  0  1    4    4
;; 1 Mazda RX4 Wag  21   6  160 110  3.9 2.875 17.02  0  1    4    4

We can now refer to mtcars:model

mtcars:model
#("Mazda RX4" "Mazda RX4 Wag" "Datsun 710" "Hornet 4 Drive" "Hornet Sportabout"
  "Valiant" "Duster 360" "Merc 240D" "Merc 230" "Merc 280" "Merc 280C"
  "Merc 450SE" "Merc 450SL" "Merc 450SLC" "Cadillac Fleetwood"
  "Lincoln Continental" "Chrysler Imperial" "Fiat 128" "Honda Civic"
  "Toyota Corolla" "Toyota Corona" "Dodge Challenger" "AMC Javelin"
  "Camaro Z28" "Pontiac Firebird" "Fiat X1-9" "Porsche 914-2" "Lotus Europa"
  "Ford Pantera L" "Ferrari Dino" "Maserati Bora" "Volvo 142E")

Replace columns

Columns are “setf-able” places and the simplest way to replace a column is set the field to a new value. We’ll complement the sex field of *d*:

(df::setf (df:column *d* 'sex) #("Female" "Female" "Male" "Female" "Male"))
;#("Female" "Female" "Male" "Female" "Male")

Note that df::setf is not exported. Use this with caution.

You can also replace a column using two functions specifically for this purpose. Here we’ll replace the ‘age’ column with new values:

(replace-column *d* 'age #(10 15 20 25 30))
;;   SEX    AGE HEIGHT WEIGHT
;; 0 Female  10    180   75.2
;; 1 Female  15    182   88.5
;; 2 Male    20    165   49.4
;; 3 Female  25    167   78.1
;; 4 Male    30    170   79.4

That was a non-destructive replacement, and since we didn’t reassign the value of *d*, it is unchanged:

LS-USER> *d*
;;   SEX    AGE HEIGHT WEIGHT
;; 0 Female  30    180   75.2
;; 1 Female  31    182   88.5
;; 2 Male    32    165   49.4
;; 3 Female  22    167   78.1
;; 4 Male    45    170   79.4

We can also use the destructive version to make a permanent change instead of setf-ing *d*:

(replace-column! *d* 'age #(10 15 20 25 30))
;;   SEX    AGE HEIGHT WEIGHT
;; 0 Female  10    180   75.2
;; 1 Female  15    182   88.5
;; 2 Male    20    165   49.4
;; 3 Female  25    167   78.1
;; 4 Male    30    170   79.4

Transform columns

There are two functions for column transformations.

replace-column

replace-column can be used to transform a column by applying a function. This example will add 20 to each value of the age column:

(replace-column *d* 'age #'(lambda (x) (+ 20 x)))
;;   SEX    AGE HEIGHT WEIGHT
;; 0 Female  30    180   75.2
;; 1 Female  35    182   88.5
;; 2 Male    40    165   49.4
;; 3 Female  45    167   78.1
;; 4 Male    50    170   79.4

replace-column! can also apply functions to a column, destructively modifying the column.

map-columns

The map-columns functions can be thought of as applying a function on all the values of each variable as a vector, rather than the individual rows as replace-column does. To see this, we’ll use functions that operate on vectors, in this case nu:e+, which is the vector addition function for Lisp-Stat. Let’s see this working first:

(nu:e+ #(1 1 1) #(2 3 4))
; => #(3 4 5)

observe how the vectors were added element-wise. We’ll demonstrate map-columns by adding one to each of the numeric columns in the example data frame:

(map-columns (select *d* t '(weight age height))
	     #'(lambda (x)
		     (nu:e+ 1 x)))
;;   WEIGHT AGE HEIGHT
;; 0   76.2  11    181
;; 1   89.5  16    183
;; 2   50.4  21    166
;; 3   79.1  26    168
;; 4   80.4  31    171

recall that we used the non-destructive version of replace-column above, so *d* has the original values. Also note the use of select to get the numeric variables from the data frame; e+ can’t add categorical values like gender/sex.

Row operations

As the name suggests, row operations operate on each row, or observation, of a data set.

count-rows

This function is used to determine how many rows meet a certain condition. For example if you want to know how many cars have a MPG (miles-per-galleon) rating greater than 20, you could use:

(use-package 'mtcars)
(count-rows mtcars 'mtcars:mpg #'(lambda (x) (< 20 x)))
; => 14

Notice the first line (use-package 'mtcars). This makes all of the symbols that name variables accessible in the LS-USER package. For large projects, you might want to configure the data frame package, for example importing CL and doing your work from there. This is mostly useful when you have several large, complicated datasets and want to work with all of them at the REPL.

do-rows

do-rows applies a function on selected variables. The function must take the same number of arguments as variables supplied. It is analogous to dotimes, but iterating over data frame rows. No values are returned; it is purely for side-effects. Let’s create a new data data-frame to illustrate row operations:

LS-USER> (defparameter *d2*
                       (make-df '(a b) '(#(1 2 3) #(10 20 30))))
*D2*
LS-USER> *d2*
;;   A  B
;; 0 1 10
;; 1 2 20
;; 2 3 30

This example uses format to illustrate iterating using do-rows for side effect:

(do-rows *d2* '(a b) #'(lambda (a b) (format t "~A " (+ a b))))
11 22 33
; No value

map-rows

Where map-columns can be thought of as working through the data frame column-by-column, map-rows goes through row-by-row. Here we add the values in each row of two columns:

(map-rows *d2* '(a b) #'+)
#(11 22 33)

Since the length of this vector will always be equal to the data-frame column length, we can add the results to the data frame as a new column. Let’s see this in a real-world pattern, subtracting the mean from a column:

(add-column! *d2* 'c
           (map-rows *d2* 'b
                     #'(lambda (x) (- x (mean (select *d2* t 'b))))))
;;   A  B     C
;; 0 1 10 -10.0
;; 1 2 20   0.0
;; 2 3 30  10.0

You could also have used replace-column! in a similar manner to replace a column with normalize values.

Create subsets

This example assume you have saved the Rdataset mentioned above to a variables name mtcars.

mask-rows

mask-rows is similar to count-rows, except it returns a bit-vector for rows matching the predicate. This is useful when you want to pass the bit vector to another function, like select to retrieve only the rows matching the predicate.

(mask-rows mtcars 'mpg #'(lambda (x) (< 20 x)))
; => #*11110001100000000111100001110001

to make this into a filter:

(defparameter efficient-cars
  (select mtcars (mask-rows mtcars 'mpg #'(lambda (x) (< 20 x))) t)
  "Cars with MPG > 20")

To view them we’ll need to call the pprint function directly instead of using the print-object function we installed earlier. Otherwise, we’ll only see the first 6.

(pprint efficient-cars)
;;    MODEL           MPG CYL  DISP  HP DRAT    WT  QSEC VS AM GEAR CARB
;;  0 Mazda RX4      21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
;;  1 Mazda RX4 Wag  21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
;;  2 Datsun 710     22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1
;;  3 Hornet 4 Drive 21.4   6 258.0 110 3.08 3.215 19.44  1  0    3    1
;;  4 Merc 240D      24.4   4 146.7  62 3.69 3.190 20.00  1  0    4    2
;;  5 Merc 230       22.8   4 140.8  95 3.92 3.150 22.90  1  0    4    2
;;  6 Fiat 128       32.4   4  78.7  66 4.08 2.200 19.47  1  1    4    1
;;  7 Honda Civic    30.4   4  75.7  52 4.93 1.615 18.52  1  1    4    2
;;  8 Toyota Corolla 33.9   4  71.1  65 4.22 1.835 19.90  1  1    4    1
;;  9 Toyota Corona  21.5   4 120.1  97 3.70 2.465 20.01  1  0    3    1
;; 10 Fiat X1-9      27.3   4  79.0  66 4.08 1.935 18.90  1  1    4    1
;; 11 Porsche 914-2  26.0   4 120.3  91 4.43 2.140 16.70  0  1    5    2
;; 12 Lotus Europa   30.4   4  95.1 113 3.77 1.513 16.90  1  1    5    2
;; 13 Volvo 142E     21.4   4 121.0 109 4.11 2.780 18.60  1  1    4    2

You can mask multiple rows at the same time by using a predicate function that accepts the same number of arguments as rows you wish to mask.

The select system

select is a domain specific language (DSL) for slicing & dicing two dimensional data structures, including arrays and data frames. With select you can create data subsets by range, with sequence specifiers, bit masks and predicates. The select user manual documents this DSL.

For some additional examples of selecting columns, see column operations.

Summarising data

Often the first thing you’ll want to do with a data frame is get a quick summary. You can do that with these functions, and we’ve seen most of them used in this manual. For more information about these functions, see the data-frame api reference.

nrow data-frame
return the number of rows in data-frame
ncol data-frame
return the number of columns in data-frame
dims data-frame
return the dimensions of data-frame as a list in (rows columns) format
keys data-frame
return a vector of symbols representing column names
column-names data-frame
returns a list of strings of the column names in data-frames
head data-frame &optional n
displays the first n rows of data-frame. n defaults to 6.
tail data-frame &optional n
displays the last n rows of data-frame. n defaults to 6.

describe

describe data-frame
returns the meta-data for the variables in data-frame

describe is a common lisp function that describes an object. In Lisp-Stat describe prints a description of the data frame and the three ‘standard’ properties of the variables: type, unit and description. It is similar to the str command in R. To see an example use the augmented mtcars data set included in Lisp-Stat. In this data set, we have added properties describing the variables. This is a good illustration of why you should always save data frames in lisp format; properties such as these are lost in CSV format.

LS-USER> (load #P"LS:DATASETS;ls-mtcars")
LS-USER> (describe mtcars)
MTCARS
  Motor Trend Car Road Tests
  A data-frame with 32 observations of 12 variables

Variable | Type         | Unit | Label
-------- | ----         | ---- | -----------
MODEL    | STRING       | NIL  | NIL
MPG      | DOUBLE-FLOAT | M/G  | Miles/(US) gallon
CYL      | INTEGER      | NA   | Number of cylinders
DISP     | DOUBLE-FLOAT | IN3  | Displacement (cu.in.)
HP       | INTEGER      | HP   | Gross horsepower
DRAT     | DOUBLE-FLOAT | NA   | Rear axle ratio
WT       | DOUBLE-FLOAT | LB   | Weight (1000 lbs)
QSEC     | DOUBLE-FLOAT | S    | 1/4 mile time
VS       | BIT          | NA   | Engine (0=v-shaped, 1=straight)
AM       | BIT          | NA   | Transmission (0=automatic, 1=manual)
GEAR     | INTEGER      | NA   | Number of forward gears
CARB     | INTEGER      | NA   | Number of carburetors

summary

summary data-frame
returns a summary of the variables in data-frame

Summary functions are one of those things that tend to be use-case or application specific. Witness the number of R summary packages; there are at least half a dozen, including hmisc, stat.desc, psych describe, skim and summary tools. In short, there is no one-size-fits-all way to provide summaries, so Lisp-Stat provides the data structures upon which users can customise the summary output. The output you see below is a simple :print-function for each of the summary structure types (numeric, factor, bit and generic).

LS-USER> (summary mtcars)
(

MPG (Miles/(US) gallon)
 n: 32
 missing: 0
 min=10.40
 q25=15.40
 q50=19.20
 mean=20.09
 q75=22.80
 max=33.90

CYL (Number of cylinders)
14 (44%) x 8, 11 (34%) x 4, 7 (22%) x 6,

DISP (Displacement (cu.in.))
 n: 32
 missing: 0
 min=71.10
 q25=120.65
 q50=205.87
 mean=230.72
 q75=334.00
 max=472.00

HP (Gross horsepower)
 n: 32
 missing: 0
 min=52
 q25=96.00
 q50=123
 mean=146.69
 q75=186.25
 max=335

DRAT (Rear axle ratio)
 n: 32
 missing: 0
 min=2.76
 q25=3.08
 q50=3.70
 mean=3.60
 q75=3.95
 max=4.93

WT (Weight (1000 lbs))
 n: 32
 missing: 0
 min=1.51
 q25=2.54
 q50=3.33
 mean=3.22
 q75=3.68
 max=5.42

QSEC (1/4 mile time)
 n: 32
 missing: 0
 min=14.50
 q25=16.88
 q50=17.71
 mean=17.85
 q75=18.90
 max=22.90

VS (Engine (0=v-shaped, 1=straight))
ones: 14 (44%)

AM (Transmission (0=automatic, 1=manual))
ones: 13 (41%)

GEAR (Number of forward gears)
15 (47%) x 3, 12 (38%) x 4, 5 (16%) x 5,

CARB (Number of carburetors)
10 (31%) x 4, 10 (31%) x 2, 7 (22%) x 1, 3 (9%) x 3, 1 (3%) x 6, 1 (3%) x 8, )

Note that the model column, essentially row-name was deleted from the output. The summary function, designed for human readable output, removes variables with all unique variables, and those with monotonically increasing numbers (usually row numbers).

To build your own summary function, use the get-summaries function to get a list of summary structures for the variables in the data frame, and then print them as you wish.

columns

You can also describe or summarize individual columns:

LS-USER> (describe 'mtcars:mpg)
MTCARS:MPG
  [symbol]

MPG names a symbol macro:
  Expansion: (AREF (COLUMNS MTCARS) 1)

Symbol-plist:
  :TYPE -> DOUBLE-FLOAT
  :UNIT -> M/G
  :LABEL -> "Miles/(US) gallon"
LS-USER> (summarize-column 'mtcars:mpg)

MPG (Miles/(US) gallon)
 n: 32
 missing: 0
 min=10.40
 q25=15.40
 q50=19.20
 mean=20.09
 q75=22.80
 max=33.90

Missing values

Data sets often contain missing values and we need to both understand where and how many are missing, and how to transform or remove them for downstream operations. In Lisp-Stat, missing values are represented by the keyword symbol :na. You can control this encoding during delimited text import by passing an a-list containing the mapping. By default this is a keyword parameter map-alist:

(map-alist '((""   . :na)
             ("NA" . :na)))

The default maps blank cells ("") and ones containing “NA” (not available) to the to the keyword :na, which stands for missing. Some systems encode missing values as numeric, e.g. 99; in this case you can pass in a map-alist that includes this mapping:

(map-alist '((""   . :na)
             ("NA" . :na)
			 (99   . :na)))

We will use the R air-quality dataset to illustrate working with missing values. Let’s load it now:

(defdf aq
  (read-csv rdata:airquality))

Examine

To see missing values we use the predicate missingp. This works on sequences, arrays and data-frames. It returns a logical sequence, array or data-frame indicating which values are missing. T indicates a missing value, NIL means the value is present. Here’s an example of using missingp on a vector:

(missingp #(1 2 3 4 5 6 :na 8 9 10))
;#(NIL NIL NIL NIL NIL NIL T NIL NIL NIL)

and on a data-frame:

 (pprint (missingp aq))

;;     X3  OZONE SOLAR-R WIND TEMP MONTH DAY
;;   0 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;   1 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;   2 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;   3 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;   4 NIL     T       T NIL  NIL  NIL   NIL
;;   5 NIL   NIL       T NIL  NIL  NIL   NIL
;;   6 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;   7 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;   8 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;   9 NIL     T     NIL NIL  NIL  NIL   NIL
;;  10 NIL   NIL       T NIL  NIL  NIL   NIL
;;  11 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;  12 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;  13 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;  14 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;  15 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;  16 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;  17 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;  18 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;  19 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;  20 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;  21 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;  22 NIL   NIL     NIL NIL  NIL  NIL   NIL
;;  23 NIL   NIL     NIL NIL  NIL  NIL   NIL ..

We can see that the ozone variable contains some missing values. To see which rows of ozone are missing, we can use the which function:

(which aq:ozone :predicate #'missingp)
;#(4 9 24 25 26 31 32 33 34 35 36 38 41 42 44 45 51 52 53 54 55 56 57 58 59 60 64 71 74 82 83 101 102 106 114 118 149)

and to get a count, use the length function on this vector:

(length *) ; => 37

It’s often convenient to use the summary function to get an overview of missing values. We can do this because the missingp function is a transformation of a data-frame that yields another data-frame of boolean values:

LS-USER> (summary (missingp aq))
X4: 153 (100%) x NIL,
OZONE: 116 (76%) x NIL, 37 (24%) x T,
SOLAR-R: 146 (95%) x NIL, 7 (5%) x T,
WIND: 153 (100%) x NIL,
TEMP: 153 (100%) x NIL,
MONTH: 153 (100%) x NIL,
DAY: 153 (100%) x NIL,

we can see that ozone is missing 37 values, 24% of the total, and solar-r is missing 7 values.

Exclude

To exclude missing values from a single column, use the Common Lisp remove function:

(remove :na aq:ozone)
;#(41 36 12 18 28 23 19 8 7 16 11 14 18 14 34 6 30 11 1 11 4 32 ...

To ensure that our data-frame includes only complete observations, we exclude any row with a missing value. To do this use the drop-missing function:

(head (drop-missing aq))
;;   X3 OZONE SOLAR-R WIND TEMP MONTH DAY
;; 0  1    41     190  7.4   67     5   1
;; 1  2    36     118  8.0   72     5   2
;; 2  3    12     149 12.6   74     5   3
;; 3  4    18     313 11.5   62     5   4
;; 4  7    23     299  8.6   65     5   7
;; 5  8    19      99 13.8   59     5   8

Replace

To replace missing values we can use the transformation functions. For example we can recode the missing values in ozone by the mean. Let’s look at the first six rows of the air quality data-frame:

(head aq)
;;   X3 OZONE SOLAR-R WIND TEMP MONTH DAY
;; 0  1    41     190  7.4   67     5   1
;; 1  2    36     118  8.0   72     5   2
;; 2  3    12     149 12.6   74     5   3
;; 3  4    18     313 11.5   62     5   4
;; 4  5    NA      NA 14.3   56     5   5
;; 5  6    28      NA 14.9   66     5   6

Now replace ozone with the mean using the common lisp function nsubstitute:

(nsubstitute (mean (remove :na aq:ozone)) :na aq:ozone)

and look at head again:

(head aq)
;;   X3             OZONE SOLAR-R WIND TEMP MONTH DAY
;; 0  1           41.0000     190  7.4   67     5   1
;; 1  2           36.0000     118  8.0   72     5   2
;; 2  3           12.0000     149 12.6   74     5   3
;; 3  4           18.0000     313 11.5   62     5   4
;; 4  5           42.1293      NA 14.3   56     5   5
;; 5  6           28.0000      NA 14.9   66     5   6

You could have used the non-destructive substitute if you wanted to create a new data-frame and leave the original aq untouched.

Normally we’d round mean to be consistent from a type perspective, but did not here so you can see the values that were replaced.

Dates & times

There are several libraries for working with time. Of these, local-time is probably the best designed and supported and the one we recommend for using with Lisp-Stat. It builds on the basic date & time functions included in Common Lisp and allows you to:

  • print timestamp in various standard or custom formats (e.g. RFC1123 or RFC3339)
  • parse time strings,
  • perform time arithmetic,
  • convert Unix times, timestamps, and universal times to and fro.

local-time is available in CLPM and Quicklisp.