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:

 

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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.

 

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.

 

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