The **dim()** function in R can be used to either get or set the dimensions of an array, matrix or data frame.

The following examples show how to use this function in practice.

**Example 1: Use dim() to Get Dimensions of Data Frame**

Suppose we have the following data frame in R:

#create data frame df <- data.frame(team=c('A', 'B', 'C', 'D', 'E'), points=c(99, 90, 86, 88, 95), assists=c(33, 28, 31, 39, 34), rebounds=c(30, 28, 24, 24, 28)) #view data frame df team points assists rebounds 1 A 99 33 30 2 B 90 28 28 3 C 86 31 24 4 D 88 39 24 5 E 95 34 28

We can use the **dim()** function to retrieve the number of rows and columns in the data frame:

#get dimensions of data frame dim(df) [1] 5 4

From the output we can see that the data frame has **5** rows and **4** columns.

**Example 2: ****Use dim() to Get Dimensions of Matrix**

Suppose we have the following matrix in R:

#create matrix mat <- matrix(c(1, 4, 4, 8, 5, 4, 3, 8), nrow=4) #view matrix mat [,1] [,2] [1,] 1 5 [2,] 4 4 [3,] 4 3 [4,] 8 8

We can use the **dim()** function to retrieve the number of rows and columns in the matrix:

#get dimensions of matrix dim(mat) [1] 4 2

From the output we can see that the matrix has **4** rows and **2** columns.

**Example 3: ****Use dim() to Set Dimensions of Matrix**

We can also use **dim()** to set the dimensions of a matrix:

#create vector of values x <- c(1, 4, 4, 8, 5, 4, 3, 8) #define dimensions for values dim(x) <- c(4, 2) #view result x [,1] [,2] [1,] 1 5 [2,] 4 4 [3,] 4 3 [4,] 8 8 #view class class(x) [1] "matrix" "array"

The result is a matrix (and an array) with **4** rows and **2** columns.

**Example 4: ****Use dim() to Get One Dimension**

We can also use **dim(x)[1]** and **dim(x)[2]** to retrieve just the number of rows or just the number of columns of an object.

For example, suppose we have the following matrix:

#create matrix x <- matrix(c(1, 4, 4, 8, 5, 4, 3, 8), nrow=4) #view matrix x [,1] [,2] [1,] 1 5 [2,] 4 4 [3,] 4 3 [4,] 8 8

We can use **dim(x)[1]** to only get the number of rows:

#display number of rows in matrix dim(x)[1] [1] 4

And we can use **dim(x)[2]** to only get the number of columns:

#display number of columns in matrix dim(x)[2] [1] 2

**Additional Resources**

The following tutorials explain how to use other common functions in R:

How to Use tabulate() Function in R

How to Use length() Function in R

How to Use replicate() Function in R