The **drop()** function in base R can be used to delete the dimensions of an array or matrix that only have one level.

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

**Example 1: Use drop() to Delete Dimensions with One Level in Array**

Suppose we have the following 3-dimensional array in R:

#create 3-dimensional array my_array <- c(1:10) dim(my_array ) <- c(1,2,5) #view array my_array , , 1 [,1] [,2] [1,] 1 2 , , 2 [,1] [,2] [1,] 3 4 , , 3 [,1] [,2] [1,] 5 6 , , 4 [,1] [,2] [1,] 7 8 , , 5 [,1] [,2] [1,] 9 10

We can use the **drop()** function to drop the dimension that only has one level in the array:

#drop dimensions with only one level new_array <- drop(my_array) #view new array new_array [,1] [,2] [,3] [,4] [,5] [1,] 1 3 5 7 9 [2,] 2 4 6 8 10

Notice that the dimension with only one level has been dropped.

We can use the **dim()** function to view the new dimensions:

#view dimensions of new array dim(new_array) [1] 2 5

We can see that the new array only has two dimensions.

**Example 2: Use drop() to Delete Dimensions with One Level in Matrix**

Suppose we have the following matrix with seven columns and one row in R:

#create matrix my_matrix <- matrix(1:7, ncol=7) #view matrix my_matrix [,1] [,2] [,3] [,4] [,5] [,6] [,7] [1,] 1 2 3 4 5 6 7 #view dimensions of matrix dim(my_matrix) [1] 1 7

We can use the **drop()** function to drop the dimension that only has one level in the matrix:

#drop dimensions with only one level new_matrix <- drop(my_matrix) #view new matrix new_matrix [1] 1 2 3 4 5 6 7

Notice that the dimension with only one level has been dropped.

The matrix has effectively been converted to a vector.

If we use the **dim()** function to view the dimensions, it will return **NULL** since the new object is no longer a matrix with two dimensions:

#view dimensions of new matrix dim(new_matrix) NULL

Instead, we can use **length()** to display the length of the vector:

#view length length(new_matrix) [1] 7

We can see that our vector has 7 elements in it.

**Additional Resources**

The following tutorials explain how to perform other common tasks in R:

How to Use the cut() Function in R

How to Use n() Function in R

How to Use nchar() Function in R