R Programming/Sample Session

This page is an introduction to the R programming language. It shows how to perform very simple tasks using R. First you need to have R installed (see the Settings page). If you use Windows or Mac OS, the easiest solution is to use the R Graphical User Interface (click on its icon). If you use Linux, open a terminal and type R at the command prompt.

Usually when you open R, you see a message similar to the following in the console:

R version 2.11.1 (2010-05-31)
Copyright (C) 2010 The R Foundation for Statistical Computing
ISBN 3-900051-07-0
 
R is free software and comes with ABSOLUTELY NO WARRANTY.
You are welcome to redistribute it under certain conditions.
Type 'license()' or 'licence()' for distribution details.
 
R is a collaborative project with many contributors.
Type 'contributors()' for more information and
'citation()' on how to cite R or R packages in publications.
 
Type 'demo()' for some demos, 'help()' for on-line help, or
'help.start()' for an HTML browser interface to help.
Type 'q()' to quit R.
 
[Previously saved workspace restored]
 
>

You can type your code after the angle bracket >.

R can be used as a simple calculator and we can perform any simple computation.

 
> # Sample Session 
> # This is a comment
> 
> 2 # print a number
[1] 2
> 2+3 # perform a simple calculation
[1] 5
> log(2)
[1] 0.6931472

We can also store numeric or string objects.

> x <- 2 # store an object
> x # print this object
[1] 2
> (x <- 3) # store and print an object
[1] 3
> 
> x <- "Hello" # store a string object
> x
[1] "Hello"

We can also store vectors.

> Height <- c(168, 177, 177, 177, 178, 172, 165, 171, 178, 170) #store a vector
> Height  # print the vector
 [1] 168 177 177 177 178 172 165 171 178 170
> 
> Height[2] # Print the second component
[1] 177
> Height[2:5] # Print the second, the 3rd, the 4th and 5th component
[1] 177 177 177 178
> 
> (obs <- 1:10) # Define a vector as a sequence (1 to 10)
 [1]  1  2  3  4  5  6  7  8  9 10
> 
> Weight <- c(88, 72, 85, 52, 71, 69, 61, 61, 51, 75)
> 
> BMI <- Weight/((Height/100)^2)   # Performs a simple calculation using vectors
> BMI
 [1] 31.17914 22.98190 27.13141 16.59804 22.40879 23.32342 22.40588 20.86112
 [9] 16.09645 25.95156

We can also describe the vector with length(), mean() and var().

> length(Height)
[1] 10
> mean(Height) # Compute the sample mean
[1] 173.3
> var(Height)
[1] 22.23333

We can also define a matrix.

> M <- cbind(obs,Height,Weight,BMI) # Create a matrix
> typeof(M) # Give the type of the matrix
[1] "double"
> class(M)  # Give the class of an object
[1] "matrix"
> is.matrix(M) # Check if   M is a matrix
[1] TRUE
> is.vector(M)  # M is not a vector
[1] FALSE
> dim(M)    # Dimensions of a matrix
[1] 10  4

We can plot the data using plot().

 
> plot(Height,Weight,ylab="Weight",xlab="Height",main="Corpulence")

We can define a dataframe.

 
> mydat <- data.frame(M) # Creates a dataframe
> names(mydat) # Give the names of each variable
[1] "obs"    "Height" "Weight" "BMI"   
> str(mydat)   # give the structure of your data
'data.frame':   10 obs. of  4 variables:
 $ obs   : num  1 2 3 4 5 6 7 8 9 10
 $ Height: num  168 177 177 177 178 172 165 171 178 170
 $ Weight: num  88 72 85 52 71 69 61 61 51 75
 $ BMI   : num  31.2 23 27.1 16.6 22.4 ...
> 
> View(mydat)  # Look at your data
> 
> summary(mydat)  # Descriptive Statistics
      obs            Height          Weight           BMI       
 Min.   : 1.00   Min.   :165.0   Min.   :51.00   Min.   :16.10  
 1st Qu.: 3.25   1st Qu.:170.2   1st Qu.:61.00   1st Qu.:21.25  
 Median : 5.50   Median :174.5   Median :70.00   Median :22.70  
 Mean   : 5.50   Mean   :173.3   Mean   :68.50   Mean   :22.89  
 3rd Qu.: 7.75   3rd Qu.:177.0   3rd Qu.:74.25   3rd Qu.:25.29  
 Max.   :10.00   Max.   :178.0   Max.   :88.00   Max.   :31.18  
>

You can save an R session (all the objects in memory) and load the session.

> save.image(file="~/Documents/Logiciels/R/test.rda")
> load("~/Documents/Logiciels/R/test.rda")

We can define a working directory. Note for Windows users : R uses slash ("/") in the directory instead of backslash ("\").

> setwd("~/Desktop")            # Sets working directory (character string enclosed in "...")
> getwd()                       # Returns current working directory
[1] "/Users/username/Desktop"
> dir() * Lists the content of the working directory

There are some special characters in R

• NA : Not Available (ie missing values)
• NaN : Not a Number (eg 0/0)
• Inf: Infinity
• -Inf : Minus Infinity.

For instance 0 divided by 0 gives a NaN but 1 divided by 0 gives $+\infty$

 > 0/0
 [1] NaN
 > 1/0
 [1] Inf

We can exit R using q(). The no argument specifies that the R session is not saved.

q("no")