Count Number of List Elements in R

In this article, we will explore how to count the number of elements in a list in R, including both simple and nested lists.

We'll use two key functions:

1. length() to count the number of top-level elements in a list.
2. lengths() to count the number of elements within each top-level list component.

These functions are helpful for navigating and analyzing lists in R, especially when dealing with nested structures.

1. Creating a List

To start, we can create a basic list using vectors, character data, or range sequences. Then we use length() to count the number of top-level elements.

a1 <- list("Geeks", "For", "Geeks")
print(length(a1))

[1] 3

2. Empty List

Here, we create an empty list and count its elements, which will be 0.

empty_list <- list()
print(length(empty_list))

[1] 0

3. List with Range, Vector, and Character Vector

Here we combine numeric and character vectors into a single list and prints the total number of top level list elements.

vec <- 1:5
my_range <- seq(3, 9, by = 2)
my_list <- list(numbers = vec, sequence = my_range, fruits = c("apple", "banana", "orange"))
print(my_list)
print(length(my_list))

$numbers
[1] 1 2 3 4 5

$sequence
[1] 3 5 7 9

$fruits
[1] "apple"  "banana" "orange"

[1] 3

4. Counting Elements in Nested List Using lengths()

Now we will use lengths() function to get the number of elements inside each top level element of the list (nested lists).

values <- 10:50
names <- c("sravan", "bobby", "ojaswi", "gnanu")
data1 <- list(1, 2, 3, 4, 5)
data <- list(a1 = values, a2 = names, a3 = data1)
print(lengths(data))

a1 a2 a3 
41  4  5 

5. Using length() and lengths() simultaneously

We will try to understand the difference between length() and lengths() function by implementing the simultaneously. We can observe that:

• length(data) counts the top level elements in the list.
• lengths(data) counts the number of elements in each nested list.

data1 <- list(1, 2, 3, 4, 5)
data2 <- list("a", 'b', 'c')
data <- list(a1 = data1, a2 = data2)
return(length(data))
print("-----------------------------")
return(lengths(data))

Output:

2

[1] "-----------------------------"

a1: 5
a2: 3

sravankumar_171fa07058

Follow

Improve

Article Tags :

• R Language
• R Programs
• R-List
• R List-Programs