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In R, it is possible to convert a list to a matrix using the matrix() function. This function takes the list as an argument and returns a matrix containing the elements of the list. The resulting matrix can be customized by specifying the number of rows and columns as well as the data type for the matrix elements. Examples are provided to further explain the syntax and usage of the matrix() function.
You can use the following syntax to convert a list to a matrix in R:
#convert list to matrix (by row) matrix(unlist(my_list), ncol=3, byrow=TRUE) #convert list to matrix (by column) matrix(unlist(my_list), ncol=3)
The following examples show how to use this syntax in practice.
Example 1: Convert List to Matrix (By Rows)
The following code shows how convert a list to a matrix (by rows) in R:
#create list my_list <- list(1:3, 4:6, 7:9, 10:12, 13:15) #view list my_list [[1]] [1] 1 2 3 [[2]] [1] 4 5 6 [[3]] [1] 7 8 9 [[4]] [1] 10 11 12 [[5]] [1] 13 14 15 #convert list to matrix matrix(unlist(my_list), ncol=3, byrow=TRUE) [,1] [,2] [,3] [1,] 1 2 3 [2,] 4 5 6 [3,] 7 8 9 [4,] 10 11 12 [5,] 13 14 15
The result is a matrix with 5 rows and 3 columns.
Example 2: Convert List to Matrix (By Columns)
The following code shows how to convert a list to a matrix (by columns) in R:
#create list
my_list <- list(1:5, 6:10, 11:15)
#view list
my_list
[[1]]
[1] 1 2 3 4 5
[[2]]
[1] 6 7 8 9 10
[[3]]
[1] 11 12 13 14 15
#convert list to matrix
matrix(unlist(my_list), ncol=3)
[,1] [,2] [,3]
[1,] 1 6 11
[2,] 2 7 12
[3,] 3 8 13
[4,] 4 9 14
[5,] 5 10 15
The result is a matrix with 5 rows and 3 columns.
Cautions on Converting a List to Matrix
Note that R will throw an error if you attempt to convert a list to a matrix in which each position of the list doesn’t have the same number of elements.
The following example illustrates this point:
#create list
my_list <- list(1:5, 6:10, 11:13)
#view list
my_list
[[1]]
[1] 1 2 3 4 5
[[2]]
[1] 6 7 8 9 10
[[3]]
[1] 11 12 13
#attempt to convert list to matrix
matrix(unlist(my_list), ncol=3)
Warning message:
In matrix(unlist(my_list), ncol = 3) :
data length [13] is not a sub-multiple or multiple of the number of rows [5]
The following tutorials explain how to perform other common conversions in R: