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Table of Contents
R Cheat Sheet
R is a free software environment for statistical computing and graphics. These notes summarize the free R CodeSchool tutorial.
Basics
R
is the command-line interpreter- Expressions are evaluated and displayed e.g. 1, 1+1, “Hello World”
- Booleans are e.g.
1=1
,3>4
,TRUE
, T,FALSE
, F - For variable assignment
x=1
orx←1
- For help on a function use
help(sum)
orexample(sqrt)
- Operations are
+ - * / = ←
NA
is used to express a missing or unknown data value. Expressions on NA return NA.
Vectors
- To create a vector, use the combine command
c(4,7,9)
- Vectors must be of the same type, and are cast if not (e.g. to strings).
a:b
creates a vector of integers from a to b.seq(a,b,s)
creates a vector of numbers from a to b in increments of smyseq[3]
to access third element i.e. vectors indexed starting at 1.- Use a vector as an index to access multiple elements e.g.
myseq[c(1,3)]
- The
names
function can be used to assign names to vector elements. Once names are asigned, they can be used as indices e.g.names(myseq)=c('one','two','three') myseq['two']
myseq + 1
adds one to all elements of the myseq vector.- Scalar operations or functions on vectors typically produce other vectors e.g. + - == sin(myseq)
Plotting
barplot[myseq]
creates a bar plot of themyseq
vector.abline(h=y)
plots a horizontal line at height y.plot[x,y]
plots x vs y e.g.x=seq[0,20,.1] y=sin(x) plot(x,y)
contour(mymat)
plots a contour map of a matrix.persp(mymat)
plots a contour map in perspective.image(volcano)
generates a heat map of the matrix.
Matrices
matrix(0,3,4)
creates a 3×4 matrix with all elements 0.matrix(1:12,3,4)
creates a 3×4 matrix with numbers 1-12.- dim(myseq) can be used to change dimensions of a matrix
mymatrix[3,4]
returns an element of the matrix (row,column).mymatrix[,2]
returns entire second column.
Data Sets
factor
is a collection type for categorized values -myfac=factor(myvec)
factor
s group unique string values aslevel
s e.g. levels(myfac) shows unique levels.as.integer(myfac)
shows levels as integers, can be used to set plot typelegend(“topright”, levels(types), pch=1:length(levels(types)))
- A data frame collects sets of related values (i.e. sets of columns with values in the same order) e.g.
mydf=data.frame(weights,prices,types)
- To extract a column, use double-square brackets with the column index or name e.g.
mydf[['weights']]
or just a dollar sign e.g.treasure$prices
merge
merges data sets by joining on shared column names
Statistics
mean(myvec) median(myvec) sd(myvec)
File Handling
list.files()
to list files in furrent directorysource(“file.R”)
to load file of coderead.csv('mydat.csv')
to load a csv fileread.table
to read text data with other separators