Extract List Elements Conditionally in R (Example)

This page shows how to subset list elements based on a condition in R.

The tutorial is structured as follows:

Let’s jump right to the example:

Construction of Example Data

Consider the following example data:

my_list <- list(A = 1:5,                        # Create example list
                B = letters[7:1],
                C = "X",
                D = 10:13)
my_list                                         # Print example list
# $A
# [1] 1 2 3 4 5
# 
# $B
# [1] "g" "f" "e" "d" "c" "b" "a"
# 
# $C
# [1] "X"
# 
# $D
# [1] 10 11 12 13

Have a look at the previously shown output of the RStudio console. It visualizes that our example data is a list with four different list elements.

Example: Conditionally Subset List Using Filter() Function

This section shows how to extract specific list elements conditionally.

Let’s assume that we want to get a new list containing only list elements that have the character class.

For this task, we can use the Filter function as shown below:

Filter(function(x) is.character(x), my_list)    # Applying Filter function
# $B
# [1] "g" "f" "e" "d" "c" "b" "a"
# 
# $C
# [1] "X"

As you can see based on the previous output, we have returned a new list containing only the list elements B and C, i.e. the character strings.

Video & Further Resources

Do you need further info on the topics of this article? Then I recommend having a look at the following video of my YouTube channel. In the video, I’m illustrating the R code of this post:

Furthermore, you might want to read the other posts of my website. I have released several articles about lists already.

• Select Multiple Elements from List
• How to Add New Elements to a List
• Count Number of List Elements
• Convert Data Frame Columns to List Elements
• Extract Names of List Elements
• Introduction to R Programming

In summary: In this R programming article you have learned how to select certain elements of a list using a logical condition. In case you have any further comments or questions, please let me know in the comments section.