# How to Use the dim() Function in R

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)

 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)

 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)

 "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) and dim(x) 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) to only get the number of rows:

```#display number of rows in matrix
dim(x)

 4
```

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

```#display number of columns in matrix
dim(x)

 2
```