R - Syntax

Although the "Hello World!" program looks simple, it has all the fundamental concepts of R which is necessary to learn to proceed further. Lets start learning R programming by writing a "Hello World!" program. In R, a program can be written at command prompt directly or in a R script file. Lets learn both methods one by one.

R Command Prompt

R allows a user to perform interactive mode programming which involves executing a program by writing directly in the command line. To start interactive programming, call the R interpreter by just typing the following command at the command prompt:

$ R

After this, R interpreter will be launched with a prompt > where a program can be directly written and executed at the command line. In the example below, print "Hello World!" program is written and executed directly at the command line.

> Str <- "Hello World!"
> print(Str)
[1] "Hello World!"

Here, in the first statement a string variable Str is defined, and "Hello World!" is assigned to it using <- operator. After that print() statement is used to print the value of the variable Str.

R Script File

Generally, R programming is done by writing the program in a script file and then executing the script at command prompt with the help of R interpreter called Rscript. The script file can be created by writing the code in the text file and saving the file with the file extension .R. Lets consider a R script called test.R, containing the following code:

#First program in R
Str <- "Hello World!"

print(Str)

The script can be executed at the command prompt using following syntax:

$ Rscript test.R 

This will give the following output:

[1] "Hello World!"

R Comments

The Comments are added in programming code with the purpose of in-code documentation. It makes the code more readable and hence easier to update the code later. It starts with # and ends with the end of that line. Anything after # to the end of the line is a single line comment and will be ignored by the compiler.

Example:

The example below shows how to use comments in the R. Comments are ignored by the compiler while running the code.

# first line comment
print('Hello World!') # second line comment

The output of the above code will be:

[1] "Hello World!"