You can use the ncol() function in R to count the number of columns in a data frame or matrix.
This function uses the following basic syntax:
ncol(x)
where:
- x: Name of the data frame or matrix
The following examples show how use this function in different scenarios.
Example 1: Use ncol to Count Number of Columns in 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 ncol() function to display the total number of columns in the data frame:
#display number of columns in data frame
ncol(df)
[1] 4
From the output we can see that there are 4 total columns in the data frame.
Example 2: Use ncol to Count Number of Columns in Matrix
Suppose we have the following matrix in R:
#create matrix
mat <- matrix(1:21, nrow=3)
#view matrix
mat
[,1] [,2] [,3] [,4] [,5] [,6] [,7]
[1,] 1 4 7 10 13 16 19
[2,] 2 5 8 11 14 17 20
[3,] 3 6 9 12 15 18 21
We can use the ncol() function to display the total number of columns in the matrix:
#display number of columns in matrix
ncol(mat)
[1] 7
From the output we can see that there are 7 total columns in the matrix.
When to Use ncol Function in Practice
In practice, we often use the ncol function when we first load a new dataset into R so that we can quickly understand the size of a dataset.
This function is often used with nrow, which tells us the number of rows in a given dataset.
To quickly view the number of columns and rows in a dataset, you can use the dim function, which returns the dimensions of a dataset in terms of number of columns and rows.
The following code shows how to use these functions with a 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)) #display number of rows nrow(df) [1] 5 #display number of columns ncol(df) [1] 4 #display dimensions dim(df) [1] 5 4
From the output we can see that this data frame has 5 rows and 4 columns.
Additional Resources
The following tutorials explain how to perform other common tasks in R:
How to Use nrow Function in R
How to Select Specific Columns in R