Select First Element of Nested List in R (2 Examples)

 

In this article, I’ll show how to extract the top of each list element in a nested list in the R programming language.

The tutorial will contain two examples for the extraction of list elements. More precisely, the content of the page is structured as follows:

It’s time to dive into the R code.

 

Introducing Example Data

As a first step, we have to construct some data that we can use in the examples below.

my_list <- list(list(1, 5, 9, 1),    # Example list
                list("a", "b", "c"),
                list(5, 7, 1))
my_list                              # Print list
# [[1]]
# [[1]][[1]]
# [1] 1
# 
# [[1]][[2]]
# [1] 5
# 
# [[1]][[3]]
# [1] 9
# 
# [[1]][[4]]
# [1] 1
# 
# 
# [[2]]
# [[2]][[1]]
# [1] "a"
# 
# [[2]][[2]]
# [1] "b"
# 
# [[2]][[3]]
# [1] "c"
# 
# 
# [[3]]
# [[3]][[1]]
# [1] 5
# 
# [[3]][[2]]
# [1] 7
# 
# [[3]][[3]]
# [1] 1

As you can see based on the previous output of the RStudio console, our exemplifying data is a nested list containing three lists.

 

Example 1: Extract First Element of Nested List Using lapply Function

Example 1 shows how to use the lapply function to return the first element of each list.

lapply(my_list, `[[`, 1)             # Use lapply function
# [[1]]
# [1] 1
# 
# [[2]]
# [1] "a"
# 
# [[3]]
# [1] 5

The previous output shows the result of our R code: A list containing three elements.

 

Example 2: Extract First Element of Nested List Using purrr Package

This Section explains how to use the purrr package. We first need to install and load the purrr package:

install.packages("purrr")            # Install & load purrr package
library("purrr")

Now, we can use the map function provided by purrr:

map(my_list, 1)                      # Use map function
# [[1]]
# [1] 1
# 
# [[2]]
# [1] "a"
# 
# [[3]]
# [1] 5

The output is the same as in Example 1.

 

Video & Further Resources

Do you need further info on the R programming syntax of this article? Then you may watch the following video of my YouTube channel. I’m explaining the topics of this tutorial in the video:

 

The YouTube video will be added soon.

 

In addition, you might have a look at the other articles on my website:

 

Summary: This article explained how to return the upper element of each list object within a nested list in R programming. Let me know in the comments, in case you have additional questions.

 

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2 Comments. Leave new

  • Hi! I have a question regarding extracting specific elements from lists.

    I am working on a project at university and we have a large dataframe given… I have a list of strings reprecenting moves in chess. I would like to select the uneven numbers of each list in order to differentiate which moves are made by white and which black.

    moves_char <- as.character(droplevels(daten$moves))
    moves_split <- sapply(moves_char, FUN = strsplit, split = " ")
    ungerade <- sapply(moves_split, function(x) {seq(from = 1, to = length(x), by = 2)})

    however, it will not let me choose the uneven numbers from the list.. I'm trying to get it to select a list of uneven numbers from each element of a list. I really hope I was able to formulate this understandably!

    lapply(moves_split, FUN = "[[", sapply(moves_split, function(x) {seq(from = 1, to = length(x), by = 2)}))
    Error in FUN(X[[i]], …) :
    attempt to select more than one element in vectorIndex

    Any help would be greatly appreciated

    Reply
    • Hey Lola,

      Thank you for the kind comment. Are you still seeking for help on this question? I just came back from vacation and therefore couldn’t reply earlier.

      Regards,
      Joachim

      Reply

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