How to Count Number of Elements in List in R (With Example)


You can use the following methods to count the number of elements in a list in R:

Method 1: Count Number of Elements in List

length(my_list)

Method 2: Count Number of Elements in Specific Component of List

length(my_list[[3]])

Method 3: Count Number of Elements in Each Component of List

lengths(my_list)

The following examples show how to use each method in practice with the following list in R:

#define list
my_list <- list(x=c(1, 4, 4, 5, 7, 8),
                y='Hey',
                z=factor(c('A', 'B', 'C', 'D')))

#view list
my_list

$x
[1] 1 4 4 5 7 8

$y
[1] "Hey"

$z
[1] A B C D
Levels: A B C D

Example 1: Count Number of Elements in List

We can use the length() function to simply count how many elements are in the list:

#count number of elements in list
length(my_list)

[1] 3

We can see that there are 3 elements in the list.

Example 2: Count Number of Elements in Specific Component of List

We can use the length() function combined with double brackets to count the number of elements in a  specific component of the list.

For example, we can use the following code to count how many elements are in the third component of the list:

#count number of elements in third component of list
length(my_list[[3]])

[1] 4

We can see that there are 4 elements in the third component of the list.

Specifically, the four values are A, B, C, and D.

Example 3: Count Number of Elements in Each Component of List

We can use the lengths() function to count the number of elements in each individual component of the list:

#count number of elements in each component of list
lengths(my_list)

x y z 
6 1 4 

From the output we can see:

  • x has 6 elements (1, 4, 4, 5, 7, 8)
  • y has 1 element (‘hey’)
  • z has 4 elements (‘A’, ‘B’, ‘C’, ‘D’)

Note that we could also use the sum() function with the length() function to count the total number of individual elements in the entire list:

#count total number of individual elements in entire list
sum(lengths(my_list))

[1] 11 

We can see that there are 11 total elements in the entire list.

Additional Resources

The following tutorials explain how to use other common functions in R:

How to Use the replace() Function in R
How to Use split() Function in R
How to Use the View() Function in R

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