nrow()

nrow(x)

nrow() returns the number of rows in a matrix, array, or data frame. It returns NULL for atomic vectors since vectors have no dimensions.

Syntax

nrow(x)

Parameters

Parameter	Type	Default	Description
x	matrix, array, data frame, or NULL	—	Input object to get row count from

Examples

Basic usage with a matrix

# Create a 3x4 matrix
mat <- matrix(1:12, nrow = 3, ncol = 4)
nrow(mat)
# [1] 3

Working with data frames

df <- data.frame(
  name = c("Alice", "Bob", "Charlie"),
  age = c(25, 30, 35),
  score = c(85, 92, 78)
)

nrow(df)
# [1] 3

Using with NULL and vectors

# NULL has no dimensions
nrow(NULL)
# NULL

# Vectors have no dimensions
vec <- 1:10
nrow(vec)
# NULL

Common Patterns

Loop over rows

mat <- matrix(1:12, nrow = 3)

# Process each row
for (i in 1:nrow(mat)) {
  print(mean(mat[i, ]))
}

Check if object has rows

has_rows <- function(x) {
  !is.null(nrow(x))
}

has_rows(matrix(1:4, 2, 2))
# [1] TRUE

has_rows(1:10)
# [1] FALSE

Get last row

mat <- matrix(1:12, nrow = 3, ncol = 4)

# Get last row
mat[nrow(mat), ]
# [1]  9 10 11 12

See Also

• base::ncol
• base::dim
• base::length
• base::rownames