Learn lists in R in plain language – Lists are objects in R that contain elements of different types

Herbert Huffner R & R-Studio December 5, 2020

Lists are objects in R that contain elements of different types, such as numbers, strings, vectors, and other lists within them. A list can contain a matrix or a function as its elements.

objects in R, Lists are created using the List () function.

Create a list

The following is an example of how to create a list of logical strings, numbers, and values.

# Create a list containing strings, numbers, vectors and a logical

# values.

list_data <- list (“Red”, “Green”, c (21,32,11), TRUE, 51.23, 119.1)

print (list_data)

When we run the above code; The following results are generated:

[[1]]

[1] “Red”

[[2]]

[1] “Green”

[[3]]

[1] 21 32 11

[[4]]

[1] TRUE

[[5]]

[1] 51.23

[[6]]

[1] 119.1

Name the members of the list

List members can be named and accessed using their names.

# Create a list containing a vector, a matrix and a list.

list_data <- list (c (“Jan”, “Feb”, “Mar”), matrix (c (3,9,5,1, -2,8), nrow = 2),

list (“green”, 12.3))

# Give names to the elements in the list.

names (list_data) <- c (“1st Quarter”, “A_Matrix”, “A Inner list”)

# Show the list.

print (list_data)

When we run the above code; The following result is created:

$ `1st_Quarter`

[1] “Jan” “Feb” “Mar”

$ A_Matrix

[, 1] [, 2] [, 3]

[1,] 3 5 -2

[2,] 9 1 8

$ A_Inner_list

$ A_Inner_list [[1]]

[1] “green”

$ A_Inner_list [[2]]

[1] 12.3

Access the elements of a list

They can be accessed using the index of members of a list. In the case of named lists; They can be accessed using the names of Nir members.

We use the list in the example above; We continue:

# Create a list containing a vector, a matrix and a list.

list_data <- list (c (“Jan”, “Feb”, “Mar”), matrix (c (3,9,5,1, -2,8), nrow = 2),

list (“green”, 12.3))

# Give names to the elements in the list.

names (list_data) <- c (“1st Quarter”, “A_Matrix”, “A Inner list”)

# Access the first element of the list.

print (list_data [1])

# Access the thrid element. As it is also a list, all its elements will be printed.

print (list_data [3])

# Access the list element using the name of the element.

print (list_data $ A_Matrix)

When we run the above code; The following result is obtained:

$ `1st_Quarter`

[1] “Jan” “Feb” “Mar”

$ A_Inner_list

$ A_Inner_list [[1]]

[1] “green”

$ A_Inner_list [[2]]

[1] 12.3

[, 1] [, 2] [, 3]

[1,] 3 5 -2

[2,] 9 1 8

Hire members of a list

We can list the elements as shown below; Add or remove. We can only add elements to the bottom of the list; Also, we can only delete the elements at the bottom of a list. But we can update any element.

# Create a list containing a vector, a matrix and a list.

list_data <- list (c (“Jan”, “Feb”, “Mar”), matrix (c (3,9,5,1, -2,8), nrow = 2),

list (“green”, 12.3))

# Give names to the elements in the list.

names (list_data) <- c (“1st Quarter”, “A_Matrix”, “A Inner list”)

# Add element at the end of the list.

list_data [4] <- “New element”

print (list_data [4])

# Remove the last element.

list_data [4] <- NULL

# Print the 4th Element.

print (list_data [4])

# Update the 3rd Element.

list_data [3] <- “updated element”

print (list_data [3])

When we execute the above code; The following result is obtained:

[[1]]

[1] “New element”

$ <NA>

NULL

$ `A Inner list`

[1] “updated element”

Merge lists

You can merge multiple lists into one list. This is done by placing all the lists in a list () function.

# Create two lists.

list1 <- list (1,2,3)

list2 <- list (“Sun”, “Mon”, “Tue”)

# Merge the two lists.

merged.list <- c (list1, list2)

# Print the merged list.

print (merged.list)

When we run the above code; The following result is obtained:

[[1]]

[1] 1

[[2]]

[1] ۲

[[3]]

[1] 3

[[4]]

[1] “Sun”

[[5]]

[1] “Mon”

[[6]]

[1] “Tue”

Convert list to vector

A list can be turned into a vector; In such a way that the elements of that vector can be used for future use. All arithmetic operations on vectors can be performed after the list has been converted to vectors; Applied. To perform this conversion, we use the unlist () function . This function takes the list as input and generates a vector.

# Create lists.

list1 <- list (1: 5)

print (list1)

list2 <-list (10:14)

print (list2)

# Convert the lists to vectors.

v1 <- unlist (list1)

v2 <- unlist (list2)

print (v1)

print (v2)

# Now add the vectors

result <- v1 + v2

print (result)