dim() function gets or sets the dimension of a matrix, array or data frame.

dim(x)

x: array, matrix or data frame.

>BOD #R Biochemical Oxygen Demand Dataset

Time demand
1 1 8.3
2 2 10.3
3 3 19.0
4 4 16.0
5 5 15.6
6 7 19.8

>class(BOD)

[1] "data.frame"

>dim(BOD) #get dimension

[1] 6 2

Set dimension of a matrix:

>x <- rep(1:20)
>x

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

Set dimension to 2 × 5:

>dim(x) <- c(2,5)
>x

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