What is R in computing?

R is a “language and environment for statistical computing and graphics”. R is an integrated suite of facilities for data manipulation, calculation and graphical display.

Among other things it has:

• An effective data handling and storage facility
• A suite of operators for calculations on arrays
• A large, coherent, integrated collection of intermediate tools for data analysis
• Graphical facilities for data analysis and display either directly at the computer or on hard-copy

R is very much a vehicle for newly developing methods of interactive data analysis. It has developed rapidly, and has been extended by a large collection of packages.*

How to work under R

Step 1. In your bash window, create a new working sub-directory (we recommend you use separate working directories for analyses conducted with R, here under Desktop), and move to it

$ cd Desktop
$ mkdir exerciseR 
$ cd exerciseR

Step 2. Start the R program by simply typing R

$ R

This command will open the R environment for you, and a new prompt will appear: “>”

Step 3. To work under R, write any command following the “>” prompt as in Unix

> 

Example of basic operations in R:

> x = 3
> y = 2
> x + y
[1] 5

Step 4. R being created for statistical purposes, it has very helpful built-in functions

> sqrt(3 * 4 + 2 * 5 + 3)
[1] 5
> log(5) + log(10)
[1] 3.912023
> log(50) 
[1] 3.912023
> sum(3 * 4 + 2 * 5 + 3)
[1] 25

Where sqrt=square root, …

Step 5. When working under your current R session, the entities (variables, functions, etc…) that R (you) creates and uses are called ‘objects’.

To display the names of the objects, there are two options:

> objects() 
> ls()

Step 6. As in Unix, to remove the two ‘objects’ (in this example called x and y) you can use rm

> rm(x, y) 

Step 7. To quit R

> q() 

You will be asked whether you want to save your workspace image

> q()
Save workspace image? [y/n/c]:

Where y=yes (save data and quit), n=no (quit without saving data) and c=cancel (abort the request and continue working under the current R session).

If you choose ‘y’, your objects will be saved in an ‘.RData’ file, and the command lines in a ‘.Rhistory’ file

Important things to know

Note 1. As in Unix (man), obtaining help for functions is possible in R (help or ?). Example to obtain information on a command called sum

> help(sum)
> ?sum

To close this sub-section type “q”

Note 2. A “+” symbol might appear when you try to execute a command

+ 

This means R is expecting you to complete your command

Note 3. As Unix, R is case sensitive

> help(sum)
> HELP(sum) 

The first command will work, the second will output Error in HELP(sum): impossible to find the function “HELP”

Note 4. As for Unix, you can use the upwards arrow on your keyboard (↑) to go back to the previous command you used.

Note 5. A very detailed introduction on how to use R can be found in https://cran.r-project.org/doc/manuals/r-release/R-intro.html

_{*Please note that these are official definitions of R taken from https://www.r-project.org/ and http://mercury.webster.edu/aleshunas/R_learning_infrastructure/Introduction_to_R_and_RStudio.html)}