Convert Nested Lists to Data Frame or Matrix in R (2 Examples)

On this page, I’ll illustrate how to store a list of lists in a data frame or matrix in the R programming language.

The tutorial will consist of these topics:

Let’s jump right to the examples…

Creation of Example Data

The first step is to define some data that we can use in the examples below:

my_nested_list <- list(l1 = list(1:5,                         # Create nested list
                                 letters[3:1],
                                 "x"),
                       l2 = list(10:15,
                                 letters[13:11],
                                 "y"),
                       l3 = list("This",
                                 "is another",
                                 "list"))
my_nested_list                                                # Print nested list
# $l1
# $l1[[1]]
# [1] 1 2 3 4 5
# 
# $l1[[2]]
# [1] "c" "b" "a"
# 
# $l1[[3]]
# [1] "x"
# 
# 
# $l2
# $l2[[1]]
# [1] 10 11 12 13 14 15
# 
# $l2[[2]]
# [1] "m" "l" "k"
# 
# $l2[[3]]
# [1] "y"
# 
# 
# $l3
# $l3[[1]]
# [1] "This"
# 
# $l3[[2]]
# [1] "is another"
# 
# $l3[[3]]
# [1] "list"
# 
#

The previous output of the RStudio console shows that our example data is a nested list containing three sub-lists.

Example 1: Convert List of Lists to Data Frame by Column

This example explains how to convert our nested list to a data frame where each column of the data frame contains one of the sub-lists.

For this, we can use the do.call and cbind functions as shown below.

In the following R code we also use the as.data.frame function to convert our lists to a data frame instead of a matrix object.

Have a look at the following R code and its output:

my_list_data_cbind <- as.data.frame(do.call(cbind,            # Convert nested list to data frame by column
                                            my_nested_list))
 my_list_data_cbind # Print nested list in data frame
#              l1                     l2         l3
# 1 1, 2, 3, 4, 5 10, 11, 12, 13, 14, 15       This
# 2       c, b, a                m, l, k is another
# 3             x                      y       list

As you can see, we have created a data frame where each column contains a list.

We can now extract single lists from this data frame using the $ operator:

my_list_data_cbind$l1                                         # Print one element of nested list in data frame
# [[1]]
# [1] 1 2 3 4 5
# 
# [[2]]
# [1] "c" "b" "a"
# 
# [[3]]
# [1] "x"
#

The previous R code has printed the first sub-list of our nested list (or the first variable of our new data frame respectively) to the RStudio console.

Example 2: Convert List of Lists to Matrix by Row

Example 2 shows how to bind the sub-lists of a nested list as rows in a matrix object.

For this, we can use the do.call and rbind functions as shown below:

my_list_data_rbind <- do.call(rbind,                          # Convert nested list to matrix by row
                              my_nested_list)
my_list_data_rbind # Print nested list in matrix
#    [,1]      [,2]         [,3]  
# l1 Integer,5 Character,3  "x"   
# l2 Integer,6 Character,3  "y"   
# l3 "This"    "is another" "list"

We can now extract certain lists by subsetting our matrix:

my_list_data_rbind["l1", ]                                    # Print one element of nested list in matrix
# [[1]]
# [1] 1 2 3 4 5
# 
# [[2]]
# [1] "c" "b" "a"
# 
# [[3]]
# [1] "x"
#

Video, Further Resources & Summary

I have recently published a video on my YouTube channel, which explains how to flatten a list of lists based on the examples of this post. You can find the video tutorial below.

Also, you might read the other RStudio posts of my website. I have published several related tutorials about related topics such as data conversion, factors, character strings, matrices, and nested lists.

• Select First Element of Nested List
• Index Element of List in R
• Select Random Element from List
• Get Second Sub Entry of Every List Element
• Select Multiple Elements from List
• Introduction to R

In this tutorial you have learned how to convert and cast nested lists as data frames and matrices in the R programming language. If you have further questions, let me know in the comments.