Looping over Objects in R Programming (original) (raw)

Last Updated : 12 Jul, 2025

One of the biggest issues with the “for” loop is its memory consumption and its slowness in executing a repetitive task. When it comes to dealing with a large data set and iterating over it, a for loop is not advised.

In this article we will discuss How to loop over a list in R Programming Language provides many alternatives to be applied to vectors for looping operations that are pretty useful when working interactively on a command line.

function and its variants:

• apply()
• lapply()
• sapply()
• tapply()
• mapply()

Let us see what each of these functions does.

apply(): This function applies a given function over the margins of a given array.

apply(): This function applies a given function over the margins of a given array.

apply(array, margins, function, ...) array = list of elements margins = dimension of the array along which the function needs to be applied function = the operation which you want to perform

R `

R program to illustrate

apply() function

Creating a matrix

A = matrix(1:9, 3, 3) print(A)

Applying apply() over row of matrix

Here margin 1 is for row

r = apply(A, 1, sum) print(r)

Applying apply() over column of matrix

Here margin 2 is for column

c = apply(A, 2, sum) print(c)

`

**Output:

[, 1] [, 2] [, 3]
[1, ] 1 4 7
[2, ] 2 5 8
[3, ] 3 6 9

[1] 12 15 18
[1] 6 15 24

lapply(): This function is used to apply a function over a list. It always returns a list of the same length as the input list.

lapply(list, function, ...)
list = Created list
function = the operation which you want to perform

R `

R program to illustrate

lapply() function

Creating a matrix

A = matrix(1:9, 3, 3)

Creating another matrix

B = matrix(10:18, 3, 3)

Creating a list

myList = list(A, B)

applying lapply()

determinant = lapply(myList, det) print(determinant)

`

**Output:

[[1]]
[1] 0

[[2]]
[1] 5.329071e-15

sapply(): This function is used to simplify the result of lapply(), if possible. Unlike lapply(), the result is not always a list. The output varies in the following ways:-

sapply(list, function, ...)
list = Created list
function = the operation which you want to perform

R `

R program to illustrate

sapply() function

Creating a list

A = list(a = 1:5, b = 6:10)

applying sapply()

means = sapply(A, mean) print(means)

`

**Output:

a b
3 8

A vector is returned since the output had a list with elements of length 1.

• If output is a list containing elements having length 1, then a vector is returned.
• If output is a list where all the elements are vectors of same length(>1), then a matrix is returned.
• If output contains elements which cannot be simplified or elements of different types, a list is returned.

tapply(): This function is used to apply a function over subset of vectors given by a combination of factors.

tapply(vector, factor, function, ...)
vector = Created vector
factor = Created factor
function = the operation which you want to perform

R `

R program to illustrate

tapply() function

Creating a factor

Id = c(1, 1, 1, 1, 2, 2, 2, 3, 3)

Creating a vector

val = c(1, 2, 3, 4, 5, 6, 7, 8, 9)

applying tapply()

result = tapply(val, Id, sum) print(result)

`

**Output:

1 2 3
10 18 17

How does the above code work?

mapply(): It's a multivariate version of lapply(). This function can be applied over several list simultaneously.

mapply(function, list1, list2, ...)
function = the operation which you want to perform
list1, list2= Created lists.

R `

R program to illustrate

mapply() function

Creating a list

A = list(c(1, 2, 3, 4))

Creating another list

B = list(c(2, 5, 1, 6))

Applying mapply()

result = mapply(sum, A, B) print(result)

`

**Output:

[1] 24

**Loop Through List & Display All Sub-Elements on Same Line

R `

my_list <- c(1, 2, 3, 4, 5)

for (element in my_list) { cat(element, " ") }

`

**Output:

1 2 3 4 5

**Loop Through List & Display All Sub-Elements on Different Lines

R `

my_list <- c(1, 2, 3, 4, 5)

for (element in my_list) { cat(element, "\n") }

`

**Output:

1
2
3
4
5

**Loop Through List and Only Display Specific Values

R `

my_list <- c(1, 2, 3, 4, 5)

for (element in my_list) { if (element %% 2 == 0) { # Display only even values cat(element, "\n") } }

`

**Output:

2
4

First we creates a list my_list with values from 1 to 5. It then iterates through each element using a for loop, and if the element is even (determined by element %% 2 == 0), it is printed on a new line using cat. The output displays only the even values (2 and 4) from the list.