ncol()

ncol(x)

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

Syntax

ncol(x)

Parameters

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

Examples

Basic usage with a matrix

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

Working with data frames

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

ncol(df)
# [1] 3

Using with NULL and vectors

ncol(NULL)
# NULL

vec <- 1:10
ncol(vec)
# NULL

Common Patterns

Loop over columns

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

for (j in 1:ncol(mat)) {
  print(sum(mat[, j]))
}

Check if object has columns

has_cols <- function(x) {
  !is.null(ncol(x))
}

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

has_cols(1:10)
# [1] FALSE

Get last column

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

mat[, ncol(mat)]
# [1]  3  6  9 12

See Also

• base::nrow
• base::dim
• base::length
• base::rownames