Introduction to R - Duke University
Introduction to R
Opening R – click on icon
Changing directory to a folder for the current project – File>Change Directory
getting help:
?plot find the help file for the function or keyword
help(plot) find the help file for the function or keyword
help(“plot”) find the help file for the function or keyword
help.search("plot") find all help files that use the term “plot”
Help pulldown menu: multiple help options, including pdf manual
Command console:
Use up arrow to recall past commands
Variables:
- case sensitive
- types: integer, numeric, character, etc
Assigning values to variables
= or
Displaying values of variables – type name of variable (results not automatically displayed)
Displaying sizes of variables: length(x)
Matrices and vectors
n=numeric(100) create a one-dimensional array to store 100 numbers
n=array(0,c(nrow,ncol)) fill a nrow x ncol matrix n with zeros
n=matrix(0,nrow,ncol) same as above
n=matrix(m,nrow,ncol) fill a matrix with the elements of m
n=array(0,c(nrow,1)) fill a nrow x 1 column vector n with zeros
n=array(0,c(1,ncol)) fill a 1 x ncol row vector with zeros
n=array(0,c(nrow,ncol,ndep)) fill a nrow x ncol x ndep array with zeros
Accessing elements of matrices, arrays, or data frames:
n=array(1:12,c(3,4))
n[3,2] get the item in row 3, column 2 of n
n[3,] get the 3rd row of n
n[,2] get the 2nd column of n
n[-3,] get all but the 3rd row of n
n[,-(1:2)] get all but the 1st and 2nd columns of n
n[5] get the 5th item in n
Changing the dimensions of an array:
x=runif(16) create an array of 16 0-1 uniform random numbers
dim(x)=c(4,4)
Referring to variable Year in dataframe Data:
Data$Year
Logical statements:
&, |, , =, ==
(1 For a mix of points (small circles) and (solid, thick) lines in a graph and the corresponding legend:
include
type=c("p","l","l","l"),pch=21,col=c("black","blue","green","red"),lty=1,lwd=2
in the matplot command
and
pch=c(21,-1,-1,-1),col=c("black","blue","green","red"), lty=c("blank","solid","solid","solid"),lwd=2
in the legend command
[because there are no point characters with the code -1, the command pch=c(21,-1,-1,-1) tricks the legend function into not drawing points for the last 3 entries]
Multiple graphs in 1 window:
split.screen(c(2,2))
screen(1), screen(2), etc.
Multiple graphics windows:
windows() to open a new window
dev.set(2) to return to window 2 (the first one opened)
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