How to Use the nrow() Function in R

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The nrow() function in R is “used to get the rows for an object“. The nrow() function can easily extract the number of rows in an object that can be a matrix, data frame, or even a dataset.

Syntax

nrow(data)

Parameters

The data is a required argument that can be vector, array, data frame, NULL, or matrix.

Return value

It returns the number of rows of an input R object.

Example 1: Counting the number of rows in the Data Frame

Create a data frame using the data.frame() function.

Use the nrow() function to count the number of rows in a data frame.

df <- data.frame(
  students = c("Michael", "Taylor", "Selena"),
  marks = c(90, 80, 75),
  levels = c(10, 7, 8)
)

nrow(df)

Output

[1] 3

Our data frame has three rows and three columns, and we get the three rows using the nrow() function.

Example 2: Counting the number of rows of the matrix in R

To count the number of rows of a matrix in R, use the nrow() function.

mat <- matrix(1:9, 3, 3)

print(mat)

cat("---Couting number of rows of a matrix---", "\n")

nrow(mat)

Output

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

---Couting number of rows of a matrix---

[1] 3

You can see that the nrow() function returns three as output because the matrix has three rows.

Example 3: Counting the number of rows of an array in R

Use the nrow() function to count the number of rows of an array in R.

arr <- array(1:12, dim = 4:3)

print(arr)

cat("---Counting number of rows using nrow() function---", "\n")

nrow(arr)

Output

     [,1] [,2] [,3]
[1,]   1   5    9
[2,]   2   6   10
[3,]   3   7   11
[4,]   4   8   12

---Counting number of rows using nrow() function---

[1] 4

You can see that the array has four rows and three columns, and its output is the same.

Example 4: nrow() function with a condition in R

To use the nrow() function with a condition in R, use the subsetting.

The subsetting approach helps us filter some data based on the condition.

df <- data.frame(LETTERS, letters, position = 1:length(letters))

dfSubset <- df[6:10, ]

nrow(dfSubset)

Output

[1] 5

Let’s use the iris dataset and apply a condition while fetching the number of rows of the data frame.

nrow(iris[iris$Sepal.Length > 3, ])

Output

[1] 150

You can see that the iris dataset has 150 rows whose Sepal.Length is greater than 3.

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