for loop

A for loop is used to iterate over a vector, in R programming.

Syntax of for loop

for (val in sequence) {
    statement
}

Here, sequence is a vector and val takes on each of its value during the loop. In each iteration, statement is evaluated.

Flowchart of for loop

Example of for loop

Below is an example to count the number of even numbers in a vector.

x <- c(2,5,3,9,8,11,6)
count <- 0
for (val in x) {
    if(val %% 2 == 0)  count = count+1
}
print(count)

Output

[1] 3

In the above example, the loop iterates 7 times as the vector x has 7 elements. In each iteration, val takes on the value of corresponding element of x. We have used a counter to count the number of even numbers in x. We can see that x contains 3 even numbers.