Index Element of List in R (3 Examples)

 

This tutorial shows how to return certain list elements using indices in the R programming language.

Table of contents:

Let’s dive into it!

 

Creation of Example Data

The following data will be used as basement for this R tutorial:

my_list <- list(1:5,        # Create example list
                data.frame(x1 = 9:5,
                           x2 = letters[1:5]),
                list(1:3,
                     letters[8:6]))
my_list                     # Print example list
# [[1]]
# [1] 1 2 3 4 5
# 
# [[2]]
#   x1 x2
# 1  9  a
# 2  8  b
# 3  7  c
# 4  6  d
# 5  5  e
# 
# [[3]]
# [[3]][[1]]
# [1] 1 2 3
# 
# [[3]][[2]]
# [1] "h" "g" "f"
# 
#

As you can see based on the previous output of the RStudio console, our example data is a list with three list items.

The first element of our list is a numeric vector, the second element is a data frame, and the third element is a nested list.

 

Example 1: Select Entire List Element

In Example 1, I’ll illustrate how to get an entire list element using double square brackets (i.e. “[[]]”).

The following R code returns the second element of our list, i.e. the data frame shown in Table 1:

my_list[[2]]                # Subset entire list element

 

table 1 data frame index element list

 

Example 2: Select Sub-Element of List

In Example 2, I’ll illustrate how to return an element contained in a sub-element of our list.

The following R code extracts the value in the third row and second column of the data frame stored as second list element:

my_list[[2]][3, 2]          # Subset sub-element of list element
# [1] "c"

 

Example 3: Select Nested List

This example shows how to extract values from a nested list in R.

Have a look at the following R code:

my_list[[3]][[2]]           # Subset sub_list in list
# [1] "h" "g" "f"

The first double brackets extract the third list element and the second double brackets extract the second list element of the nested list.

 

Video, Further Resources & Summary

Have a look at the following video which I have published on my YouTube channel. In the video, I illustrate the R code of this tutorial:

 

The YouTube video will be added soon.

 

Furthermore, you may want to read some of the other tutorials of my website.

 

To summarize: At this point you should know how to extract a list element based on an index in the R programming language. In case you have additional comments or questions, don’t hesitate to let me know in the comments section.

 

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