You can use the sweep() function in R to perform some operation on either the rows or columns of a matrix.
This function uses the following basic syntax:
sweep(x, MARGIN, STATS, FUN)
where:
- x: Name of the matrix
- MARGIN: The margin to perform function on (1=rows, 2=columns)
- STATS: The value(s) to use in the function
- FUN: The function to perform
The following examples show how to use the sweep() function in different scenarios in R.
Example 1: Use sweep() to Perform Operation on Rows
The following code shows how to use the sweep() function to add a specific number to the values in each row of the matrix:
#define matrix
mat <- matrix(1:15, nrow=5)
#view matrix
mat
[,1] [,2] [,3]
[1,] 1 6 11
[2,] 2 7 12
[3,] 3 8 13
[4,] 4 9 14
[5,] 5 10 15
#add specific numbers to each row
sweep(mat, 1, c(5, 10, 15, 20, 25), "+")
[,1] [,2] [,3]
[1,] 6 11 16
[2,] 12 17 22
[3,] 18 23 28
[4,] 24 29 34
[5,] 30 35 40
Here’s how the sweep() function worked in this scenario:
- 5 was added to each value in the first row.
- 10 was added to each value in the second row.
- 15 was added to each value in the third row.
- 20 was added to each value in the fourth row.
- 25 was added to each value in the fifth row.
Note that in this example we used addition (+) as the mathematical operation to perform, but we could choose to use a different operation.
For example, the following code shows how to multiply the values in each row by certain numbers:
#define matrix
mat <- matrix(1:15, nrow=5)
#view matrix
mat
[,1] [,2] [,3]
[1,] 1 6 11
[2,] 2 7 12
[3,] 3 8 13
[4,] 4 9 14
[5,] 5 10 15
#multiply values in each row by certain amount
sweep(mat, 1, c(.5, 1, 2, 4, 6), "*")
[,1] [,2] [,3]
[1,] 0.5 3 5.5
[2,] 2.0 7 12.0
[3,] 6.0 16 26.0
[4,] 16.0 36 56.0
[5,] 30.0 60 90.0
Example 2: Use sweep() to Perform Operation on Columns
The following code shows how to use the sweep() function to add a specific number to the values in each column of the matrix:
#define matrix
mat <- matrix(1:15, nrow=5)
#view matrix
mat
[,1] [,2] [,3]
[1,] 1 6 11
[2,] 2 7 12
[3,] 3 8 13
[4,] 4 9 14
[5,] 5 10 15
#add specific numbers to each column
sweep(mat, 2, c(5, 10, 15), "+")
[,1] [,2] [,3]
[1,] 6 16 26
[2,] 7 17 27
[3,] 8 18 28
[4,] 9 19 29
[5,] 10 20 30
Here’s how the sweep() function worked in this scenario:
- 5 was added to each value in the first column.
- 10 was added to each value in the second column.
- 15 was added to each value in the third column.
Additional Resources
The following tutorials explain how to perform other common operations in R:
How to Create an Empty Matrix in R
How to Convert Data Frame to Matrix in R
How to Plot the Rows of a Matrix in R