Named List in R Programming

Last Updated : 22 Jun, 2020

A list is an object in R Language which consists of heterogeneous elements. A list can even contain matrices, data frames, or functions as its elements. The list can be created using list() function in R. Named list is also created with the same function by specifying the names of the elements to access them. Named list can also be created using names() function to specify the names of elements after defining the list. In this article, we’ll learn to create named list in R using two different methods and different operations that can be performed on named lists.

Syntax: names(x) <- value

Parameters:
x: represents an R object
value: represents names that has to be given to elements of x object

Creating a Named List

A Named list can be created by two methods. The first one is by allocating the names to the elements while defining the list and another method is by using names() function.

Example 1:
In this example, we are going to create a named list without using names() function.

# Defining a list with names 
x <- list(mt = matrix(1:6, nrow = 2), 
          lt = letters[1:8], 
          n = c(1:10)) 
  
# Print whole list 
cat("Whole List:\n") 
print(x) 

Output:

Whole List:
$mt
     [,1] [,2] [,3]
[1,]    1    3    5
[2,]    2    4    6

$lt
[1] "a" "b" "c" "d" "e" "f" "g" "h"

$n
 [1]  1  2  3  4  5  6  7  8  9 10

Example 2:
In this example, we are going to define the names of elements of the list using names() function after defining the list.

# Defining list 
x <- list(matrix(1:6, nrow = 2), 
          letters[1:8], 
          c(1:10)) 
  
# Print whole list 
cat("Whole list:\n") 
print(x)

Output:

Whole list:
[[1]]
     [,1] [,2] [,3]
[1,]    1    3    5
[2,]    2    4    6

[[2]]
[1] "a" "b" "c" "d" "e" "f" "g" "h"

[[3]]
 [1]  1  2  3  4  5  6  7  8  9 10

Accessing components of Named List

Components of a named list can be easily accessed by $ operator.

Example:

# Defining a list with names 
x <- list(mt = matrix(1:6, nrow = 2), 
          lt = letters[1:8], 
          n = c(1:10)) 
  
# Print list elements using the names given 
# Prints element of the list named "mt" 
cat("Element named 'mt':\n") 
print(x$mt) 
cat("\n") 
  
# Print element of the list named "n" 
cat("Element named 'n':\n") 
print(x$n)

Output:

Element named 'mt':
     [,1] [,2] [,3]
[1,]    1    3    5
[2,]    2    4    6

Element named 'n':
 [1]  1  2  3  4  5  6  7  8  9 10

Modifying components of Named List

Components of named list can be modified by assigning new values to them.

Example:

# Defining a named list 
lt <- list(a = 1, 
           let = letters[1:8], 
           mt = matrix(1:6, nrow = 2)) 
  
cat("List before modifying:\n") 
print(lt) 
  
# Modifying element named 'a' 
lt$a <- 5 
  
cat("List after modifying:\n") 
print(lt)

Output:

List before modifying:
$a
[1] 1

$let
[1] "a" "b" "c" "d" "e" "f" "g" "h"

$mt
     [,1] [,2] [,3]
[1,]    1    3    5
[2,]    2    4    6

List after modifying:
$a
[1] 5

$let
[1] "a" "b" "c" "d" "e" "f" "g" "h"

$mt
     [,1] [,2] [,3]
[1,]    1    3    5
[2,]    2    4    6

Deleting components from Named List

To delete elements from named list, we’ll use within() function and the result will be assigned to the named list itself.

Example:

# Defining a named list 
lt <- list(a = 1, 
           let = letters[1:8], 
           mt = matrix(1:6, nrow = 2)) 
  
cat("List before deleting:\n") 
print(lt) 
  
# Modifying element named 'a' 
lt <- within(lt, rm(a)) 
  
cat("List after deleting:\n") 
print(lt)

Output:

List before deleting:
$a
[1] 1

$let
[1] "a" "b" "c" "d" "e" "f" "g" "h"

$mt
     [,1] [,2] [,3]
[1,]    1    3    5
[2,]    2    4    6

List after deleting:
$let
[1] "a" "b" "c" "d" "e" "f" "g" "h"

$mt
     [,1] [,2] [,3]
[1,]    1    3    5
[2,]    2    4    6