Find Elements in List in R (2 Examples)

In this tutorial, I’ll demonstrate how to identify list elements containing particular values in the R programming language.

The table of content is structured like this:

Let’s dive right in!

Example Data

The first step is to create some example data:

my_list <- list(1:5,                                                # Create example list
                letters[1:5],
                "a",
                letters[2:5])
my_list                                                             # Print example list
# [[1]]
# [1] 1 2 3 4 5
# 
# [[2]]
# [1] "a" "b" "c" "d" "e"
# 
# [[3]]
# [1] "a"
# 
# [[4]]
# [1] "b" "c" "d" "e"

The previous output of the RStudio console shows that our example data is a list with four list elements.

Example 1: Find List Elements that Contain Certain Value

In this section, I’ll show how to identify the index positions of all list elements that contain a particular value.

For this task, we can use the which and sapply functions as shown below:

which(sapply(my_list, function(x) "a" %in% x))                      # Index positions of matches
# [1] 2 3

The previous R code has returned the values 2 and 3, i.e. the index positions of list elements that contain the letter “a”.

Example 2: Create Subset of List Elements that Contain Certain Value

In this example, I’ll explain how to create a list subset of list elements that contain a certain value.

Have a look at the following R code:

my_list_subset <- my_list[sapply(my_list, function(x) "a" %in% x)]  # Subset of list
my_list_subset                                                      # Print subset
# [[1]]
# [1] "a" "b" "c" "d" "e"
# 
# [[2]]
# [1] "a"

As you can see, we have created a new list that contains only those two list elements that contain the letter “a”.

Video, Further Resources & Summary

Have a look at the following video on my YouTube channel. In the video, I’m explaining the topics of this tutorial in a live session:

In addition to the video, you might read the related articles which I have published on my website. Please find some tutorials on related topics such as extracting data, data inspection, data conversion, and lists below.

• Find Common Elements from Multiple Vectors
• Convert Data Frame Columns to List Elements
• Extract Names of List Elements
• Extract List Elements Conditionally in R
• Introduction to R

In this article you have learned how to find all list elements that contain a specific values in the R programming language. If you have further comments and/or questions, don’t hesitate to tell me about it in the comments.