Reference card for R
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This document provides a concise reference card summarizing common functions and operations in R including getting help, input and output, data creation, slicing and extracting data, variable conversion and information, data selection and manipulation, math operations, matrices, strings, dates and times, and plotting. It covers essential functions for loading and saving data, accessing documentation, basic data manipulation and common statistical analyses in R.
![R Reference Card
by Tom Short, EPRI PEAC, tshort@epri-peac.com 2004-11-07
Granted to the public domain. See www.Rpad.org for the source and latest
version. Includes material from R for Beginners by Emmanuel Paradis (with
permission).
Getting help
Most R functions have online documentation.
help(topic) documentation on topic
?topic id.
help.search("topic") search the help system
apropos("topic") the names of all objects in the search list matching
the regular expression ”topic”
help.start() start the HTML version of help
str(a) display the internal *str*ucture of an R object
summary(a) gives a “summary” of a, usually a statistical summary but it is
generic meaning it has different operations for different classes of a
ls() show objects in the search path; specify pat="pat" to search on a
pattern
ls.str() str() for each variable in the search path
dir() show files in the current directory
methods(a) shows S3 methods of a
methods(class=class(a)) lists all the methods to handle objects of
class a
Input and output
load() load the datasets written with save
data(x) loads specified data sets
library(x) load add-on packages
read.table(file) reads a file in table format and creates a data
frame from it; the default separator sep="" is any whitespace; use
header=TRUE to read the first line as a header of column names; use
as.is=TRUE to prevent character vectors from being converted to fac-
tors; use comment.char="" to prevent "#" from being interpreted as
a comment; use skip=n to skip n lines before reading data; see the
help for options on row naming, NA treatment, and others
read.csv("filename",header=TRUE) id. but with defaults set for
reading comma-delimited files
read.delim("filename",header=TRUE) id. but with defaults set
for reading tab-delimited files
read.fwf(file,widths,header=FALSE,sep="",as.is=FALSE)
read a table of fixed width formatted data into a ’data.frame’; widths
is an integer vector, giving the widths of the fixed-width fields
save(file,...) saves the specified objects (...) in the XDR platform-
independent binary format
save.image(file) saves all objects
cat(..., file="", sep=" ") prints the arguments after coercing to
character; sep is the character separator between arguments
print(a, ...) prints its arguments; generic, meaning it can have differ-
ent methods for different objects
format(x,...) format an R object for pretty printing
write.table(x,file="",row.names=TRUE,col.names=TRUE,
sep=" ") prints x after converting to a data frame; if quote is TRUE,
character or factor columns are surrounded by quotes ("); sep is the
field separator; eol is the end-of-line separator; na is the string for
missing values; use col.names=NA to add a blank column header to
get the column headers aligned correctly for spreadsheet input
sink(file) output to file, until sink()
Most of the I/O functions have a file argument. This can often be a charac-
ter string naming a file or a connection. file="" means the standard input or
output. Connections can include files, pipes, zipped files, and R variables.
On windows, the file connection can also be used with description =
"clipboard". To read a table copied from Excel, use
x <- read.delim("clipboard")
To write a table to the clipboard for Excel, use
write.table(x,"clipboard",sep="t",col.names=NA)
For database interaction, see packages RODBC, DBI, RMySQL, RPgSQL, and
ROracle. See packages XML, hdf5, netCDF for reading other file formats.
Data creation
c(...) generic function to combine arguments with the default forming a
vector; with recursive=TRUE descends through lists combining all
elements into one vector
from:to generates a sequence; “:” has operator priority; 1:4 + 1 is “2,3,4,5”
seq(from,to) generates a sequence by= specifies increment; length=
specifies desired length
seq(along=x) generates 1, 2, ..., length(along); useful for for
loops
rep(x,times) replicate x times; use each= to repeat “each” el-
ement of x each times; rep(c(1,2,3),2) is 1 2 3 1 2 3;
rep(c(1,2,3),each=2) is 1 1 2 2 3 3
data.frame(...) create a data frame of the named or unnamed
arguments; data.frame(v=1:4,ch=c("a","B","c","d"),n=10);
shorter vectors are recycled to the length of the longest
list(...) create a list of the named or unnamed arguments;
list(a=c(1,2),b="hi",c=3i);
array(x,dim=) array with data x; specify dimensions like
dim=c(3,4,2); elements of x recycle if x is not long enough
matrix(x,nrow=,ncol=) matrix; elements of x recycle
factor(x,levels=) encodes a vector x as a factor
gl(n,k,length=n*k,labels=1:n) generate levels (factors) by spec-
ifying the pattern of their levels; k is the number of levels, and n is
the number of replications
expand.grid() a data frame from all combinations of the supplied vec-
tors or factors
rbind(...) combine arguments by rows for matrices, data frames, and
others
cbind(...) id. by columns
Slicing and extracting data
Indexing vectors
x[n] nth element
x[-n] all but the nth element
x[1:n] first n elements
x[-(1:n)] elements from n+1 to the end
x[c(1,4,2)] specific elements
x["name"] element named "name"
x[x > 3] all elements greater than 3
x[x > 3 & x < 5] all elements between 3 and 5
x[x %in% c("a","and","the")] elements in the given set
Indexing lists
x[n] list with elements n
x[[n]] nth element of the list
x[["name"]] element of the list named "name"
x$name id.
Indexing matrices
x[i,j] element at row i, column j
x[i,] row i
x[,j] column j
x[,c(1,3)] columns 1 and 3
x["name",] row named "name"
Indexing data frames (matrix indexing plus the following)
x[["name"]] column named "name"
x$name id.
Variable conversion
as.array(x), as.data.frame(x), as.numeric(x),
as.logical(x), as.complex(x), as.character(x),
... convert type; for a complete list, use methods(as)
Variable information
is.na(x), is.null(x), is.array(x), is.data.frame(x),
is.numeric(x), is.complex(x), is.character(x),
... test for type; for a complete list, use methods(is)
length(x) number of elements in x
dim(x) Retrieve or set the dimension of an object; dim(x) <- c(3,2)
dimnames(x) Retrieve or set the dimension names of an object
nrow(x) number of rows; NROW(x) is the same but treats a vector as a one-
row matrix
ncol(x) and NCOL(x) id. for columns
class(x) get or set the class of x; class(x) <- "myclass"
unclass(x) remove the class attribute of x
attr(x,which) get or set the attribute which of x
attributes(obj) get or set the list of attributes of obj
Data selection and manipulation
which.max(x) returns the index of the greatest element of x
which.min(x) returns the index of the smallest element of x
rev(x) reverses the elements of x
sort(x) sorts the elements of x in increasing order; to sort in decreasing
order: rev(sort(x))
cut(x,breaks) divides x into intervals (factors); breaks is the number
of cut intervals or a vector of cut points
match(x, y) returns a vector of the same length than x with the elements
of x which are in y (NA otherwise)
which(x == a) returns a vector of the indices of x if the comparison op-
eration is true (TRUE), in this example the values of i for which x[i]
== a (the argument of this function must be a variable of mode logi-
cal)
choose(n, k) computes the combinations of k events among n repetitions
= n!/[(n−k)!k!]
na.omit(x) suppresses the observations with missing data (NA) (sup-
presses the corresponding line if x is a matrix or a data frame)
na.fail(x) returns an error message if x contains at least one NA](https://image.slidesharecdn.com/short-refcard-160608175856/85/Reference-card-for-R-1-320.jpg)
![unique(x) if x is a vector or a data frame, returns a similar object but with
the duplicate elements suppressed
table(x) returns a table with the numbers of the differents values of x
(typically for integers or factors)
subset(x, ...) returns a selection of x with respect to criteria (...,
typically comparisons: x$V1 < 10); if x is a data frame, the option
select gives the variables to be kept or dropped using a minus sign
sample(x, size) resample randomly and without replacement size ele-
ments in the vector x, the option replace = TRUE allows to resample
with replacement
prop.table(x,margin=) table entries as fraction of marginal table
Math
sin,cos,tan,asin,acos,atan,atan2,log,log10,exp
max(x) maximum of the elements of x
min(x) minimum of the elements of x
range(x) id. then c(min(x), max(x))
sum(x) sum of the elements of x
diff(x) lagged and iterated differences of vector x
prod(x) product of the elements of x
mean(x) mean of the elements of x
median(x) median of the elements of x
quantile(x,probs=) sample quantiles corresponding to the given prob-
abilities (defaults to 0,.25,.5,.75,1)
weighted.mean(x, w) mean of x with weights w
rank(x) ranks of the elements of x
var(x) or cov(x) variance of the elements of x (calculated on n−1); if x is
a matrix or a data frame, the variance-covariance matrix is calculated
sd(x) standard deviation of x
cor(x) correlation matrix of x if it is a matrix or a data frame (1 if x is a
vector)
var(x, y) or cov(x, y) covariance between x and y, or between the
columns of x and those of y if they are matrices or data frames
cor(x, y) linear correlation between x and y, or correlation matrix if they
are matrices or data frames
round(x, n) rounds the elements of x to n decimals
log(x, base) computes the logarithm of x with base base
scale(x) if x is a matrix, centers and reduces the data; to center only use
the option center=FALSE, to reduce only scale=FALSE (by default
center=TRUE, scale=TRUE)
pmin(x,y,...) a vector which ith element is the minimum of x[i],
y[i], ...
pmax(x,y,...) id. for the maximum
cumsum(x) a vector which ith element is the sum from x[1] to x[i]
cumprod(x) id. for the product
cummin(x) id. for the minimum
cummax(x) id. for the maximum
union(x,y), intersect(x,y), setdiff(x,y), setequal(x,y),
is.element(el,set) “set” functions
Re(x) real part of a complex number
Im(x) imaginary part
Mod(x) modulus; abs(x) is the same
Arg(x) angle in radians of the complex number
Conj(x) complex conjugate
convolve(x,y) compute the several kinds of convolutions of two se-
quences
fft(x) Fast Fourier Transform of an array
mvfft(x) FFT of each column of a matrix
filter(x,filter) applies linear filtering to a univariate time series or
to each series separately of a multivariate time series
Many math functions have a logical parameter na.rm=FALSE to specify miss-
ing data (NA) removal.
Matrices
t(x) transpose
diag(x) diagonal
%*% matrix multiplication
solve(a,b) solves a %*% x = b for x
solve(a) matrix inverse of a
rowsum(x) sum of rows for a matrix-like object; rowSums(x) is a faster
version
colsum(x), colSums(x) id. for columns
rowMeans(x) fast version of row means
colMeans(x) id. for columns
Advanced data processing
apply(X,INDEX,FUN=) a vector or array or list of values obtained by
applying a function FUN to margins (INDEX) of X
lapply(X,FUN) apply FUN to each element of the list X
tapply(X,INDEX,FUN=) apply FUN to each cell of a ragged array given
by X with indexes INDEX
by(data,INDEX,FUN) apply FUN to data frame data subsetted by INDEX
merge(a,b) merge two data frames by common columns or row names
xtabs(a b,data=x) a contingency table from cross-classifying factors
aggregate(x,by,FUN) splits the data frame x into subsets, computes
summary statistics for each, and returns the result in a convenient
form; by is a list of grouping elements, each as long as the variables
in x
stack(x, ...) transform data available as separate columns in a data
frame or list into a single column
unstack(x, ...) inverse of stack()
reshape(x, ...) reshapes a data frame between ’wide’ format with
repeated measurements in separate columns of the same record and
’long’ format with the repeated measurements in separate records;
use (direction=”wide”) or (direction=”long”)
Strings
paste(...) concatenate vectors after converting to character; sep= is the
string to separate terms (a single space is the default); collapse= is
an optional string to separate “collapsed” results
substr(x,start,stop) substrings in a character vector; can also as-
sign, as substr(x, start, stop) <- value
strsplit(x,split) split x according to the substring split
grep(pattern,x) searches for matches to pattern within x; see ?regex
gsub(pattern,replacement,x) replacement of matches determined
by regular expression matching sub() is the same but only replaces
the first occurrence.
tolower(x) convert to lowercase
toupper(x) convert to uppercase
match(x,table) a vector of the positions of first matches for the elements
of x among table
x %in% table id. but returns a logical vector
pmatch(x,table) partial matches for the elements of x among table
nchar(x) number of characters
Dates and Times
The class Date has dates without times. POSIXct has dates and times, includ-
ing time zones. Comparisons (e.g. >), seq(), and difftime() are useful.
Date also allows + and −. ?DateTimeClasses gives more information. See
also package chron.
as.Date(s) and as.POSIXct(s) convert to the respective class;
format(dt) converts to a string representation. The default string
format is “2001-02-21”. These accept a second argument to specify a
format for conversion. Some common formats are:
%a, %A Abbreviated and full weekday name.
%b, %B Abbreviated and full month name.
%d Day of the month (01–31).
%H Hours (00–23).
%I Hours (01–12).
%j Day of year (001–366).
%m Month (01–12).
%M Minute (00–59).
%p AM/PM indicator.
%S Second as decimal number (00–61).
%U Week (00–53); the first Sunday as day 1 of week 1.
%w Weekday (0–6, Sunday is 0).
%W Week (00–53); the first Monday as day 1 of week 1.
%y Year without century (00–99). Don’t use.
%Y Year with century.
%z (output only.) Offset from Greenwich; -0800 is 8 hours west of.
%Z (output only.) Time zone as a character string (empty if not available).
Where leading zeros are shown they will be used on output but are optional
on input. See ?strftime.
Plotting
plot(x) plot of the values of x (on the y-axis) ordered on the x-axis
plot(x, y) bivariate plot of x (on the x-axis) and y (on the y-axis)
hist(x) histogram of the frequencies of x
barplot(x) histogram of the values of x; use horiz=FALSE for horizontal
bars
dotchart(x) if x is a data frame, plots a Cleveland dot plot (stacked plots
line-by-line and column-by-column)
pie(x) circular pie-chart
boxplot(x) “box-and-whiskers” plot
sunflowerplot(x, y) id. than plot() but the points with similar coor-
dinates are drawn as flowers which petal number represents the num-
ber of points
stripplot(x) plot of the values of x on a line (an alternative to
boxplot() for small sample sizes)
coplot(x˜y | z) bivariate plot of x and y for each value or interval of
values of z
interaction.plot (f1, f2, y) if f1 and f2 are factors, plots the
means of y (on the y-axis) with respect to the values of f1 (on the
x-axis) and of f2 (different curves); the option fun allows to choose
the summary statistic of y (by default fun=mean)](https://image.slidesharecdn.com/short-refcard-160608175856/85/Reference-card-for-R-2-320.jpg)
![matplot(x,y) bivariate plot of the first column of x vs. the first one of y,
the second one of x vs. the second one of y, etc.
fourfoldplot(x) visualizes, with quarters of circles, the association be-
tween two dichotomous variables for different populations (x must
be an array with dim=c(2, 2, k), or a matrix with dim=c(2, 2) if
k = 1)
assocplot(x) Cohen–Friendly graph showing the deviations from inde-
pendence of rows and columns in a two dimensional contingency ta-
ble
mosaicplot(x) ‘mosaic’ graph of the residuals from a log-linear regres-
sion of a contingency table
pairs(x) if x is a matrix or a data frame, draws all possible bivariate plots
between the columns of x
plot.ts(x) if x is an object of class "ts", plot of x with respect to time, x
may be multivariate but the series must have the same frequency and
dates
ts.plot(x) id. but if x is multivariate the series may have different dates
and must have the same frequency
qqnorm(x) quantiles of x with respect to the values expected under a nor-
mal law
qqplot(x, y) quantiles of y with respect to the quantiles of x
contour(x, y, z) contour plot (data are interpolated to draw the
curves), x and y must be vectors and z must be a matrix so that
dim(z)=c(length(x), length(y)) (x and y may be omitted)
filled.contour(x, y, z) id. but the areas between the contours are
coloured, and a legend of the colours is drawn as well
image(x, y, z) id. but with colours (actual data are plotted)
persp(x, y, z) id. but in perspective (actual data are plotted)
stars(x) if x is a matrix or a data frame, draws a graph with segments or a
star where each row of x is represented by a star and the columns are
the lengths of the segments
symbols(x, y, ...) draws, at the coordinates given by x and y, sym-
bols (circles, squares, rectangles, stars, thermometres or “boxplots”)
which sizes, colours ... are specified by supplementary arguments
termplot(mod.obj) plot of the (partial) effects of a regression model
(mod.obj)
The following parameters are common to many plotting functions:
add=FALSE if TRUE superposes the plot on the previous one (if it exists)
axes=TRUE if FALSE does not draw the axes and the box
type="p" specifies the type of plot, "p": points, "l": lines, "b": points
connected by lines, "o": id. but the lines are over the points, "h":
vertical lines, "s": steps, the data are represented by the top of the
vertical lines, "S": id. but the data are represented by the bottom of
the vertical lines
xlim=, ylim= specifies the lower and upper limits of the axes, for exam-
ple with xlim=c(1, 10) or xlim=range(x)
xlab=, ylab= annotates the axes, must be variables of mode character
main= main title, must be a variable of mode character
sub= sub-title (written in a smaller font)
Low-level plotting commands
points(x, y) adds points (the option type= can be used)
lines(x, y) id. but with lines
text(x, y, labels, ...) adds text given by labels at coordi-
nates (x,y); a typical use is: plot(x, y, type="n"); text(x, y,
names)
mtext(text, side=3, line=0, ...) adds text given by text in
the margin specified by side (see axis() below); line specifies the
line from the plotting area
segments(x0, y0, x1, y1) draws lines from points (x0,y0) to points
(x1,y1)
arrows(x0, y0, x1, y1, angle= 30, code=2) id. with arrows
at points (x0,y0) if code=2, at points (x1,y1) if code=1, or both if
code=3; angle controls the angle from the shaft of the arrow to the
edge of the arrow head
abline(a,b) draws a line of slope b and intercept a
abline(h=y) draws a horizontal line at ordinate y
abline(v=x) draws a vertical line at abcissa x
abline(lm.obj) draws the regression line given by lm.obj
rect(x1, y1, x2, y2) draws a rectangle which left, right, bottom, and
top limits are x1, x2, y1, and y2, respectively
polygon(x, y) draws a polygon linking the points with coordinates given
by x and y
legend(x, y, legend) adds the legend at the point (x,y) with the sym-
bols given by legend
title() adds a title and optionally a sub-title
axis(side, vect) adds an axis at the bottom (side=1), on the left (2),
at the top (3), or on the right (4); vect (optional) gives the abcissa (or
ordinates) where tick-marks are drawn
rug(x) draws the data x on the x-axis as small vertical lines
locator(n, type="n", ...) returns the coordinates (x,y) after the
user has clicked n times on the plot with the mouse; also draws sym-
bols (type="p") or lines (type="l") with respect to optional graphic
parameters (...); by default nothing is drawn (type="n")
Graphical parameters
These can be set globally with par(...); many can be passed as parameters
to plotting commands.
adj controls text justification (0 left-justified, 0.5 centred, 1 right-justified)
bg specifies the colour of the background (ex. : bg="red", bg="blue", ...
the list of the 657 available colours is displayed with colors())
bty controls the type of box drawn around the plot, allowed values are: "o",
"l", "7", "c", "u" ou "]" (the box looks like the corresponding char-
acter); if bty="n" the box is not drawn
cex a value controlling the size of texts and symbols with respect to the de-
fault; the following parameters have the same control for numbers on
the axes, cex.axis, the axis labels, cex.lab, the title, cex.main,
and the sub-title, cex.sub
col controls the color of symbols and lines; use color names: "red", "blue"
see colors() or as "#RRGGBB"; see rgb(), hsv(), gray(), and
rainbow(); as for cex there are: col.axis, col.lab, col.main,
col.sub
font an integer which controls the style of text (1: normal, 2: italics, 3:
bold, 4: bold italics); as for cex there are: font.axis, font.lab,
font.main, font.sub
las an integer which controls the orientation of the axis labels (0: parallel to
the axes, 1: horizontal, 2: perpendicular to the axes, 3: vertical)
lty controls the type of lines, can be an integer or string (1: "solid",
2: "dashed", 3: "dotted", 4: "dotdash", 5: "longdash", 6:
"twodash", or a string of up to eight characters (between "0" and
"9") which specifies alternatively the length, in points or pixels, of
the drawn elements and the blanks, for example lty="44" will have
the same effect than lty=2
lwd a numeric which controls the width of lines, default 1
mar a vector of 4 numeric values which control the space between the axes
and the border of the graph of the form c(bottom, left, top,
right), the default values are c(5.1, 4.1, 4.1, 2.1)
mfcol a vector of the form c(nr,nc) which partitions the graphic window
as a matrix of nr lines and nc columns, the plots are then drawn in
columns
mfrow id. but the plots are drawn by row
pch controls the type of symbol, either an integer between 1 and 25, or any
single character within ""
q1 2 3 4 5 6 7 8 9 q10 11 12 q13 14 15
q16 17 18 q19 q20 q21 22 23 24 25 ** . XX aa ??
ps an integer which controls the size in points of texts and symbols
pty a character which specifies the type of the plotting region, "s": square,
"m": maximal
tck a value which specifies the length of tick-marks on the axes as a fraction
of the smallest of the width or height of the plot; if tck=1 a grid is
drawn
tcl a value which specifies the length of tick-marks on the axes as a fraction
of the height of a line of text (by default tcl=-0.5)
xaxt if xaxt="n" the x-axis is set but not drawn (useful in conjonction with
axis(side=1, ...))
yaxt if yaxt="n" the y-axis is set but not drawn (useful in conjonction with
axis(side=2, ...))
Lattice (Trellis) graphics
xyplot(y˜x) bivariate plots (with many functionalities)
barchart(y˜x) histogram of the values of y with respect to those of x
dotplot(y˜x) Cleveland dot plot (stacked plots line-by-line and column-
by-column)
densityplot(˜x) density functions plot
histogram(˜x) histogram of the frequencies of x
bwplot(y˜x) “box-and-whiskers” plot
qqmath(˜x) quantiles of x with respect to the values expected under a the-
oretical distribution
stripplot(y˜x) single dimension plot, x must be numeric, y may be a
factor
qq(y˜x) quantiles to compare two distributions, x must be numeric, y may
be numeric, character, or factor but must have two ‘levels’
splom(˜x) matrix of bivariate plots
parallel(˜x) parallel coordinates plot
levelplot(z˜x*y|g1*g2) coloured plot of the values of z at the coor-
dinates given by x and y (x, y and z are all of the same length)
wireframe(z˜x*y|g1*g2) 3d surface plot
cloud(z˜x*y|g1*g2) 3d scatter plot](https://image.slidesharecdn.com/short-refcard-160608175856/85/Reference-card-for-R-3-320.jpg)
Reference card for R
- 1. R Reference Card by Tom Short, EPRI PEAC, [email protected] 2004-11-07 Granted to the public domain. See www.Rpad.org for the source and latest version. Includes material from R for Beginners by Emmanuel Paradis (with permission). Getting help Most R functions have online documentation. help(topic) documentation on topic ?topic id. help.search("topic") search the help system apropos("topic") the names of all objects in the search list matching the regular expression ”topic” help.start() start the HTML version of help str(a) display the internal *str*ucture of an R object summary(a) gives a “summary” of a, usually a statistical summary but it is generic meaning it has different operations for different classes of a ls() show objects in the search path; specify pat="pat" to search on a pattern ls.str() str() for each variable in the search path dir() show files in the current directory methods(a) shows S3 methods of a methods(class=class(a)) lists all the methods to handle objects of class a Input and output load() load the datasets written with save data(x) loads specified data sets library(x) load add-on packages read.table(file) reads a file in table format and creates a data frame from it; the default separator sep="" is any whitespace; use header=TRUE to read the first line as a header of column names; use as.is=TRUE to prevent character vectors from being converted to fac- tors; use comment.char="" to prevent "#" from being interpreted as a comment; use skip=n to skip n lines before reading data; see the help for options on row naming, NA treatment, and others read.csv("filename",header=TRUE) id. but with defaults set for reading comma-delimited files read.delim("filename",header=TRUE) id. but with defaults set for reading tab-delimited files read.fwf(file,widths,header=FALSE,sep="",as.is=FALSE) read a table of fixed width formatted data into a ’data.frame’; widths is an integer vector, giving the widths of the fixed-width fields save(file,...) saves the specified objects (...) in the XDR platform- independent binary format save.image(file) saves all objects cat(..., file="", sep=" ") prints the arguments after coercing to character; sep is the character separator between arguments print(a, ...) prints its arguments; generic, meaning it can have differ- ent methods for different objects format(x,...) format an R object for pretty printing write.table(x,file="",row.names=TRUE,col.names=TRUE, sep=" ") prints x after converting to a data frame; if quote is TRUE, character or factor columns are surrounded by quotes ("); sep is the field separator; eol is the end-of-line separator; na is the string for missing values; use col.names=NA to add a blank column header to get the column headers aligned correctly for spreadsheet input sink(file) output to file, until sink() Most of the I/O functions have a file argument. This can often be a charac- ter string naming a file or a connection. file="" means the standard input or output. Connections can include files, pipes, zipped files, and R variables. On windows, the file connection can also be used with description = "clipboard". To read a table copied from Excel, use x <- read.delim("clipboard") To write a table to the clipboard for Excel, use write.table(x,"clipboard",sep="t",col.names=NA) For database interaction, see packages RODBC, DBI, RMySQL, RPgSQL, and ROracle. See packages XML, hdf5, netCDF for reading other file formats. Data creation c(...) generic function to combine arguments with the default forming a vector; with recursive=TRUE descends through lists combining all elements into one vector from:to generates a sequence; “:” has operator priority; 1:4 + 1 is “2,3,4,5” seq(from,to) generates a sequence by= specifies increment; length= specifies desired length seq(along=x) generates 1, 2, ..., length(along); useful for for loops rep(x,times) replicate x times; use each= to repeat “each” el- ement of x each times; rep(c(1,2,3),2) is 1 2 3 1 2 3; rep(c(1,2,3),each=2) is 1 1 2 2 3 3 data.frame(...) create a data frame of the named or unnamed arguments; data.frame(v=1:4,ch=c("a","B","c","d"),n=10); shorter vectors are recycled to the length of the longest list(...) create a list of the named or unnamed arguments; list(a=c(1,2),b="hi",c=3i); array(x,dim=) array with data x; specify dimensions like dim=c(3,4,2); elements of x recycle if x is not long enough matrix(x,nrow=,ncol=) matrix; elements of x recycle factor(x,levels=) encodes a vector x as a factor gl(n,k,length=n*k,labels=1:n) generate levels (factors) by spec- ifying the pattern of their levels; k is the number of levels, and n is the number of replications expand.grid() a data frame from all combinations of the supplied vec- tors or factors rbind(...) combine arguments by rows for matrices, data frames, and others cbind(...) id. by columns Slicing and extracting data Indexing vectors x[n] nth element x[-n] all but the nth element x[1:n] first n elements x[-(1:n)] elements from n+1 to the end x[c(1,4,2)] specific elements x["name"] element named "name" x[x > 3] all elements greater than 3 x[x > 3 & x < 5] all elements between 3 and 5 x[x %in% c("a","and","the")] elements in the given set Indexing lists x[n] list with elements n x[[n]] nth element of the list x[["name"]] element of the list named "name" x$name id. Indexing matrices x[i,j] element at row i, column j x[i,] row i x[,j] column j x[,c(1,3)] columns 1 and 3 x["name",] row named "name" Indexing data frames (matrix indexing plus the following) x[["name"]] column named "name" x$name id. Variable conversion as.array(x), as.data.frame(x), as.numeric(x), as.logical(x), as.complex(x), as.character(x), ... convert type; for a complete list, use methods(as) Variable information is.na(x), is.null(x), is.array(x), is.data.frame(x), is.numeric(x), is.complex(x), is.character(x), ... test for type; for a complete list, use methods(is) length(x) number of elements in x dim(x) Retrieve or set the dimension of an object; dim(x) <- c(3,2) dimnames(x) Retrieve or set the dimension names of an object nrow(x) number of rows; NROW(x) is the same but treats a vector as a one- row matrix ncol(x) and NCOL(x) id. for columns class(x) get or set the class of x; class(x) <- "myclass" unclass(x) remove the class attribute of x attr(x,which) get or set the attribute which of x attributes(obj) get or set the list of attributes of obj Data selection and manipulation which.max(x) returns the index of the greatest element of x which.min(x) returns the index of the smallest element of x rev(x) reverses the elements of x sort(x) sorts the elements of x in increasing order; to sort in decreasing order: rev(sort(x)) cut(x,breaks) divides x into intervals (factors); breaks is the number of cut intervals or a vector of cut points match(x, y) returns a vector of the same length than x with the elements of x which are in y (NA otherwise) which(x == a) returns a vector of the indices of x if the comparison op- eration is true (TRUE), in this example the values of i for which x[i] == a (the argument of this function must be a variable of mode logi- cal) choose(n, k) computes the combinations of k events among n repetitions = n!/[(n−k)!k!] na.omit(x) suppresses the observations with missing data (NA) (sup- presses the corresponding line if x is a matrix or a data frame) na.fail(x) returns an error message if x contains at least one NA
- 2. unique(x) if x is a vector or a data frame, returns a similar object but with the duplicate elements suppressed table(x) returns a table with the numbers of the differents values of x (typically for integers or factors) subset(x, ...) returns a selection of x with respect to criteria (..., typically comparisons: x$V1 < 10); if x is a data frame, the option select gives the variables to be kept or dropped using a minus sign sample(x, size) resample randomly and without replacement size ele- ments in the vector x, the option replace = TRUE allows to resample with replacement prop.table(x,margin=) table entries as fraction of marginal table Math sin,cos,tan,asin,acos,atan,atan2,log,log10,exp max(x) maximum of the elements of x min(x) minimum of the elements of x range(x) id. then c(min(x), max(x)) sum(x) sum of the elements of x diff(x) lagged and iterated differences of vector x prod(x) product of the elements of x mean(x) mean of the elements of x median(x) median of the elements of x quantile(x,probs=) sample quantiles corresponding to the given prob- abilities (defaults to 0,.25,.5,.75,1) weighted.mean(x, w) mean of x with weights w rank(x) ranks of the elements of x var(x) or cov(x) variance of the elements of x (calculated on n−1); if x is a matrix or a data frame, the variance-covariance matrix is calculated sd(x) standard deviation of x cor(x) correlation matrix of x if it is a matrix or a data frame (1 if x is a vector) var(x, y) or cov(x, y) covariance between x and y, or between the columns of x and those of y if they are matrices or data frames cor(x, y) linear correlation between x and y, or correlation matrix if they are matrices or data frames round(x, n) rounds the elements of x to n decimals log(x, base) computes the logarithm of x with base base scale(x) if x is a matrix, centers and reduces the data; to center only use the option center=FALSE, to reduce only scale=FALSE (by default center=TRUE, scale=TRUE) pmin(x,y,...) a vector which ith element is the minimum of x[i], y[i], ... pmax(x,y,...) id. for the maximum cumsum(x) a vector which ith element is the sum from x[1] to x[i] cumprod(x) id. for the product cummin(x) id. for the minimum cummax(x) id. for the maximum union(x,y), intersect(x,y), setdiff(x,y), setequal(x,y), is.element(el,set) “set” functions Re(x) real part of a complex number Im(x) imaginary part Mod(x) modulus; abs(x) is the same Arg(x) angle in radians of the complex number Conj(x) complex conjugate convolve(x,y) compute the several kinds of convolutions of two se- quences fft(x) Fast Fourier Transform of an array mvfft(x) FFT of each column of a matrix filter(x,filter) applies linear filtering to a univariate time series or to each series separately of a multivariate time series Many math functions have a logical parameter na.rm=FALSE to specify miss- ing data (NA) removal. Matrices t(x) transpose diag(x) diagonal %*% matrix multiplication solve(a,b) solves a %*% x = b for x solve(a) matrix inverse of a rowsum(x) sum of rows for a matrix-like object; rowSums(x) is a faster version colsum(x), colSums(x) id. for columns rowMeans(x) fast version of row means colMeans(x) id. for columns Advanced data processing apply(X,INDEX,FUN=) a vector or array or list of values obtained by applying a function FUN to margins (INDEX) of X lapply(X,FUN) apply FUN to each element of the list X tapply(X,INDEX,FUN=) apply FUN to each cell of a ragged array given by X with indexes INDEX by(data,INDEX,FUN) apply FUN to data frame data subsetted by INDEX merge(a,b) merge two data frames by common columns or row names xtabs(a b,data=x) a contingency table from cross-classifying factors aggregate(x,by,FUN) splits the data frame x into subsets, computes summary statistics for each, and returns the result in a convenient form; by is a list of grouping elements, each as long as the variables in x stack(x, ...) transform data available as separate columns in a data frame or list into a single column unstack(x, ...) inverse of stack() reshape(x, ...) reshapes a data frame between ’wide’ format with repeated measurements in separate columns of the same record and ’long’ format with the repeated measurements in separate records; use (direction=”wide”) or (direction=”long”) Strings paste(...) concatenate vectors after converting to character; sep= is the string to separate terms (a single space is the default); collapse= is an optional string to separate “collapsed” results substr(x,start,stop) substrings in a character vector; can also as- sign, as substr(x, start, stop) <- value strsplit(x,split) split x according to the substring split grep(pattern,x) searches for matches to pattern within x; see ?regex gsub(pattern,replacement,x) replacement of matches determined by regular expression matching sub() is the same but only replaces the first occurrence. tolower(x) convert to lowercase toupper(x) convert to uppercase match(x,table) a vector of the positions of first matches for the elements of x among table x %in% table id. but returns a logical vector pmatch(x,table) partial matches for the elements of x among table nchar(x) number of characters Dates and Times The class Date has dates without times. POSIXct has dates and times, includ- ing time zones. Comparisons (e.g. >), seq(), and difftime() are useful. Date also allows + and −. ?DateTimeClasses gives more information. See also package chron. as.Date(s) and as.POSIXct(s) convert to the respective class; format(dt) converts to a string representation. The default string format is “2001-02-21”. These accept a second argument to specify a format for conversion. Some common formats are: %a, %A Abbreviated and full weekday name. %b, %B Abbreviated and full month name. %d Day of the month (01–31). %H Hours (00–23). %I Hours (01–12). %j Day of year (001–366). %m Month (01–12). %M Minute (00–59). %p AM/PM indicator. %S Second as decimal number (00–61). %U Week (00–53); the first Sunday as day 1 of week 1. %w Weekday (0–6, Sunday is 0). %W Week (00–53); the first Monday as day 1 of week 1. %y Year without century (00–99). Don’t use. %Y Year with century. %z (output only.) Offset from Greenwich; -0800 is 8 hours west of. %Z (output only.) Time zone as a character string (empty if not available). Where leading zeros are shown they will be used on output but are optional on input. See ?strftime. Plotting plot(x) plot of the values of x (on the y-axis) ordered on the x-axis plot(x, y) bivariate plot of x (on the x-axis) and y (on the y-axis) hist(x) histogram of the frequencies of x barplot(x) histogram of the values of x; use horiz=FALSE for horizontal bars dotchart(x) if x is a data frame, plots a Cleveland dot plot (stacked plots line-by-line and column-by-column) pie(x) circular pie-chart boxplot(x) “box-and-whiskers” plot sunflowerplot(x, y) id. than plot() but the points with similar coor- dinates are drawn as flowers which petal number represents the num- ber of points stripplot(x) plot of the values of x on a line (an alternative to boxplot() for small sample sizes) coplot(x˜y | z) bivariate plot of x and y for each value or interval of values of z interaction.plot (f1, f2, y) if f1 and f2 are factors, plots the means of y (on the y-axis) with respect to the values of f1 (on the x-axis) and of f2 (different curves); the option fun allows to choose the summary statistic of y (by default fun=mean)
- 3. matplot(x,y) bivariate plot of the first column of x vs. the first one of y, the second one of x vs. the second one of y, etc. fourfoldplot(x) visualizes, with quarters of circles, the association be- tween two dichotomous variables for different populations (x must be an array with dim=c(2, 2, k), or a matrix with dim=c(2, 2) if k = 1) assocplot(x) Cohen–Friendly graph showing the deviations from inde- pendence of rows and columns in a two dimensional contingency ta- ble mosaicplot(x) ‘mosaic’ graph of the residuals from a log-linear regres- sion of a contingency table pairs(x) if x is a matrix or a data frame, draws all possible bivariate plots between the columns of x plot.ts(x) if x is an object of class "ts", plot of x with respect to time, x may be multivariate but the series must have the same frequency and dates ts.plot(x) id. but if x is multivariate the series may have different dates and must have the same frequency qqnorm(x) quantiles of x with respect to the values expected under a nor- mal law qqplot(x, y) quantiles of y with respect to the quantiles of x contour(x, y, z) contour plot (data are interpolated to draw the curves), x and y must be vectors and z must be a matrix so that dim(z)=c(length(x), length(y)) (x and y may be omitted) filled.contour(x, y, z) id. but the areas between the contours are coloured, and a legend of the colours is drawn as well image(x, y, z) id. but with colours (actual data are plotted) persp(x, y, z) id. but in perspective (actual data are plotted) stars(x) if x is a matrix or a data frame, draws a graph with segments or a star where each row of x is represented by a star and the columns are the lengths of the segments symbols(x, y, ...) draws, at the coordinates given by x and y, sym- bols (circles, squares, rectangles, stars, thermometres or “boxplots”) which sizes, colours ... are specified by supplementary arguments termplot(mod.obj) plot of the (partial) effects of a regression model (mod.obj) The following parameters are common to many plotting functions: add=FALSE if TRUE superposes the plot on the previous one (if it exists) axes=TRUE if FALSE does not draw the axes and the box type="p" specifies the type of plot, "p": points, "l": lines, "b": points connected by lines, "o": id. but the lines are over the points, "h": vertical lines, "s": steps, the data are represented by the top of the vertical lines, "S": id. but the data are represented by the bottom of the vertical lines xlim=, ylim= specifies the lower and upper limits of the axes, for exam- ple with xlim=c(1, 10) or xlim=range(x) xlab=, ylab= annotates the axes, must be variables of mode character main= main title, must be a variable of mode character sub= sub-title (written in a smaller font) Low-level plotting commands points(x, y) adds points (the option type= can be used) lines(x, y) id. but with lines text(x, y, labels, ...) adds text given by labels at coordi- nates (x,y); a typical use is: plot(x, y, type="n"); text(x, y, names) mtext(text, side=3, line=0, ...) adds text given by text in the margin specified by side (see axis() below); line specifies the line from the plotting area segments(x0, y0, x1, y1) draws lines from points (x0,y0) to points (x1,y1) arrows(x0, y0, x1, y1, angle= 30, code=2) id. with arrows at points (x0,y0) if code=2, at points (x1,y1) if code=1, or both if code=3; angle controls the angle from the shaft of the arrow to the edge of the arrow head abline(a,b) draws a line of slope b and intercept a abline(h=y) draws a horizontal line at ordinate y abline(v=x) draws a vertical line at abcissa x abline(lm.obj) draws the regression line given by lm.obj rect(x1, y1, x2, y2) draws a rectangle which left, right, bottom, and top limits are x1, x2, y1, and y2, respectively polygon(x, y) draws a polygon linking the points with coordinates given by x and y legend(x, y, legend) adds the legend at the point (x,y) with the sym- bols given by legend title() adds a title and optionally a sub-title axis(side, vect) adds an axis at the bottom (side=1), on the left (2), at the top (3), or on the right (4); vect (optional) gives the abcissa (or ordinates) where tick-marks are drawn rug(x) draws the data x on the x-axis as small vertical lines locator(n, type="n", ...) returns the coordinates (x,y) after the user has clicked n times on the plot with the mouse; also draws sym- bols (type="p") or lines (type="l") with respect to optional graphic parameters (...); by default nothing is drawn (type="n") Graphical parameters These can be set globally with par(...); many can be passed as parameters to plotting commands. adj controls text justification (0 left-justified, 0.5 centred, 1 right-justified) bg specifies the colour of the background (ex. : bg="red", bg="blue", ... the list of the 657 available colours is displayed with colors()) bty controls the type of box drawn around the plot, allowed values are: "o", "l", "7", "c", "u" ou "]" (the box looks like the corresponding char- acter); if bty="n" the box is not drawn cex a value controlling the size of texts and symbols with respect to the de- fault; the following parameters have the same control for numbers on the axes, cex.axis, the axis labels, cex.lab, the title, cex.main, and the sub-title, cex.sub col controls the color of symbols and lines; use color names: "red", "blue" see colors() or as "#RRGGBB"; see rgb(), hsv(), gray(), and rainbow(); as for cex there are: col.axis, col.lab, col.main, col.sub font an integer which controls the style of text (1: normal, 2: italics, 3: bold, 4: bold italics); as for cex there are: font.axis, font.lab, font.main, font.sub las an integer which controls the orientation of the axis labels (0: parallel to the axes, 1: horizontal, 2: perpendicular to the axes, 3: vertical) lty controls the type of lines, can be an integer or string (1: "solid", 2: "dashed", 3: "dotted", 4: "dotdash", 5: "longdash", 6: "twodash", or a string of up to eight characters (between "0" and "9") which specifies alternatively the length, in points or pixels, of the drawn elements and the blanks, for example lty="44" will have the same effect than lty=2 lwd a numeric which controls the width of lines, default 1 mar a vector of 4 numeric values which control the space between the axes and the border of the graph of the form c(bottom, left, top, right), the default values are c(5.1, 4.1, 4.1, 2.1) mfcol a vector of the form c(nr,nc) which partitions the graphic window as a matrix of nr lines and nc columns, the plots are then drawn in columns mfrow id. but the plots are drawn by row pch controls the type of symbol, either an integer between 1 and 25, or any single character within "" q1 2 3 4 5 6 7 8 9 q10 11 12 q13 14 15 q16 17 18 q19 q20 q21 22 23 24 25 ** . XX aa ?? ps an integer which controls the size in points of texts and symbols pty a character which specifies the type of the plotting region, "s": square, "m": maximal tck a value which specifies the length of tick-marks on the axes as a fraction of the smallest of the width or height of the plot; if tck=1 a grid is drawn tcl a value which specifies the length of tick-marks on the axes as a fraction of the height of a line of text (by default tcl=-0.5) xaxt if xaxt="n" the x-axis is set but not drawn (useful in conjonction with axis(side=1, ...)) yaxt if yaxt="n" the y-axis is set but not drawn (useful in conjonction with axis(side=2, ...)) Lattice (Trellis) graphics xyplot(y˜x) bivariate plots (with many functionalities) barchart(y˜x) histogram of the values of y with respect to those of x dotplot(y˜x) Cleveland dot plot (stacked plots line-by-line and column- by-column) densityplot(˜x) density functions plot histogram(˜x) histogram of the frequencies of x bwplot(y˜x) “box-and-whiskers” plot qqmath(˜x) quantiles of x with respect to the values expected under a the- oretical distribution stripplot(y˜x) single dimension plot, x must be numeric, y may be a factor qq(y˜x) quantiles to compare two distributions, x must be numeric, y may be numeric, character, or factor but must have two ‘levels’ splom(˜x) matrix of bivariate plots parallel(˜x) parallel coordinates plot levelplot(z˜x*y|g1*g2) coloured plot of the values of z at the coor- dinates given by x and y (x, y and z are all of the same length) wireframe(z˜x*y|g1*g2) 3d surface plot cloud(z˜x*y|g1*g2) 3d scatter plot
- 4. In the normal Lattice formula, y x|g1*g2 has combinations of optional con- ditioning variables g1 and g2 plotted on separate panels. Lattice functions take many of the same arguments as base graphics plus also data= the data frame for the formula variables and subset= for subsetting. Use panel= to define a custom panel function (see apropos("panel") and ?llines). Lattice functions return an object of class trellis and have to be print-ed to produce the graph. Use print(xyplot(...)) inside functions where auto- matic printing doesn’t work. Use lattice.theme and lset to change Lattice defaults. Optimization and model fitting optim(par, fn, method = c("Nelder-Mead", "BFGS", "CG", "L-BFGS-B", "SANN") general-purpose optimization; par is initial values, fn is function to optimize (normally minimize) nlm(f,p) minimize function f using a Newton-type algorithm with starting values p lm(formula) fit linear models; formula is typically of the form response termA + termB + ...; use I(x*y) + I(xˆ2) for terms made of nonlinear components glm(formula,family=) fit generalized linear models, specified by giv- ing a symbolic description of the linear predictor and a description of the error distribution; family is a description of the error distribution and link function to be used in the model; see ?family nls(formula) nonlinear least-squares estimates of the nonlinear model parameters approx(x,y=) linearly interpolate given data points; x can be an xy plot- ting structure spline(x,y=) cubic spline interpolation loess(formula) fit a polynomial surface using local fitting Many of the formula-based modeling functions have several common argu- ments: data= the data frame for the formula variables, subset= a subset of variables used in the fit, na.action= action for missing values: "na.fail", "na.omit", or a function. The following generics often apply to model fitting functions: predict(fit,...) predictions from fit based on input data df.residual(fit) returns the number of residual degrees of freedom coef(fit) returns the estimated coefficients (sometimes with their standard-errors) residuals(fit) returns the residuals deviance(fit) returns the deviance fitted(fit) returns the fitted values logLik(fit) computes the logarithm of the likelihood and the number of parameters AIC(fit) computes the Akaike information criterion or AIC Statistics aov(formula) analysis of variance model anova(fit,...) analysis of variance (or deviance) tables for one or more fitted model objects density(x) kernel density estimates of x binom.test(), pairwise.t.test(), power.t.test(), prop.test(), t.test(), ... use help.search("test") Distributions rnorm(n, mean=0, sd=1) Gaussian (normal) rexp(n, rate=1) exponential rgamma(n, shape, scale=1) gamma rpois(n, lambda) Poisson rweibull(n, shape, scale=1) Weibull rcauchy(n, location=0, scale=1) Cauchy rbeta(n, shape1, shape2) beta rt(n, df) ‘Student’ (t) rf(n, df1, df2) Fisher–Snedecor (F) (χ2) rchisq(n, df) Pearson rbinom(n, size, prob) binomial rgeom(n, prob) geometric rhyper(nn, m, n, k) hypergeometric rlogis(n, location=0, scale=1) logistic rlnorm(n, meanlog=0, sdlog=1) lognormal rnbinom(n, size, prob) negative binomial runif(n, min=0, max=1) uniform rwilcox(nn, m, n), rsignrank(nn, n) Wilcoxon’s statistics All these functions can be used by replacing the letter r with d, p or q to get, respectively, the probability density (dfunc(x, ...)), the cumulative probability density (pfunc(x, ...)), and the value of quantile (qfunc(p, ...), with 0 < p < 1). Programming function( arglist ) expr function definition return(value) if(cond) expr if(cond) cons.expr else alt.expr for(var in seq) expr while(cond) expr repeat expr break next Use braces {} around statements ifelse(test, yes, no) a value with the same shape as test filled with elements from either yes or no do.call(funname, args) executes a function call from the name of the function and a list of arguments to be passed to it