R Reference Card
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).
Help and basics
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
options(...) set or examine many global options; common ones: width,
digits,error
library(x) load add-on packages; library(help=x) lists datasets and
functions in package x.
attach(x) database xto the R search path; xcan be a list, data frame, or R
data file created with save. Use search() to show the search path.
detach(x) xfrom the R search path; xcan be a name or character string
of an object previously attached or a package.
Input and output
load() load the datasets written with save
data(x) loads specified data sets
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 convertedto fac-
tors; use comment.char="" to prevent "#" from being interpreted as
a comment; use skip=n to skip nlines 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 xafter 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(x); 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 xrecycle if xis not long enough
matrix(x,nrow=,ncol=) matrix; elements of xrecycle
factor(x,levels=) encodes a vector xas a factor
gl(n,k,length=n*k,labels=1:n) generate levels (factors) by spec-
ifying the pattern of their levels; kis the number of levels, and nis
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 lists
x[n] list with elements n
x[[n]] nth element of the list
x[["name"]] element of the list named "name"
x$name id.
Indexing vectors
x[n] nth element
x[-n] all but the nth element
x[1:n] first nelements
x[-(1:n)] elements from n+1 to the end
x[c(1,4,2)] specific elements
x["name"] element named "name"
x[x > 3] all elements greater than 3
x[x > 3 & x < 5] all elements between 3 and 5
x[x %in% c("a","and","the")] elements in the given set
Indexing matrices
x[i,j] element at row i, column j
x[i,] row i
x[,j] column j
x[,c(1,3)] columns 1 and 3
x["name",] row named "name"
Indexing data frames (matrix indexing plus the following)
x[["name"]] column named "name"
x$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 xin increasing order; to sort in decreasing
order: rev(sort(x))
cut(x,breaks) divides xinto intervals (factors); breaks is the number
of cut intervals or a vector of cut points
