How to Use the sweep Function in R (With Examples)

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: