R - For Loop

The For Loop

The for loop in R is used to iterate over a given sequence and executes a set of statements for each element in the sequence. A sequence can be any data structure like list, array, vector, and matrix etc.

Syntax

for iterating_var in sequence {
  statements
}

Flow Diagram:

For loop over list

In the example below, for loop is used to print all elements of a given list.

weekday <- list("MON", "TUE", "WED", "THU", "FRI")

#print all elements of weekday
for (day in weekday) {
  print(day)
}

The output of the above code will be:

[1] "MON"
[1] "TUE"
[1] "WED"
[1] "THU"
[1] "FRI"

For loop over vector

Similarly, it is used to print all elements of a vector.

number <- c(1:6)

#print all elements of number
for (i in number) {
  print(i)
}

The output of the above code will be:

[1] 1
[1] 2
[1] 3
[1] 4
[1] 5
[1] 6

next statement

By using next statement, the program skips the loop whenever condition is met, and brings the program to the start of loop. Please consider the example below.

number <- c(1:10)

#skips the loop for odd value of i
for (i in number) {
  if(i %% 2 == 1) 
    next
  print(i)
}

The output of the above code will be:

[1] 2
[1] 4
[1] 6
[1] 8
[1] 10

break statement

By using break statement, the program get out of the for loop when condition is met. Please consider the example below.

number <- c(1:10)

#get out of the loop when i == 5
for (i in number) {
  if(i == 5) 
    break
  print(i)
}

The output of the above code will be:

[1] 1
[1] 2
[1] 3
[1] 4