for Loops

In this lesson, we will learn another type of loop: the for loop.

We'll cover the following

Syntax of a for loop

The syntax for for loop in R language:

for(value in vector)
{
  statements
}

Let’s begin with printing every value in a vector:

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myVector <- c(1, 2+2i, "3", 4, 5+5i, "6")
for (v in myVector)
{
  print(v)
}

In the above code, the statement print(v) is executed for every element vv in the vector myVector.

A for loop is used to apply the same statements or function calls to a collection of objects.

Let’s visualize the code flow of for loop:

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Illustration for for loop
Illustration for for loop

We can also use for loop on lists the same way we do on vectors. Furthermore, for loops can be applied to matrices, as the following example demonstrates. This will also give us an idea of nested for loops.

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myMatrix <- matrix(c(1:12), nrow = 4, byrow = TRUE)
for (r in 1:nrow(myMatrix)) {
  for (c in 1:ncol(myMatrix))  
    print(paste("Row", r, "and column",c, " = ", myMatrix[r, c]))  
}

Here, the first loop

for (r in 1:nrow(myMatrix))

keeps track of the row index and the second nested for loop

for (c in 1:ncol(myMatrix))

keeps track of the column index.

The nested for loop allows us to iterate over the complete matrix one element at a time.