dim()

dim(x)

Returns integer or NULL· Updated May 12, 2026· Base Functions

dimensionsmatrixdata-framebase

dim() returns the dimensions of an array, matrix, or data frame. If the object does not have dimensions, dim() returns NULL. You can also use dim() to set dimensions on a vector, effectively converting it into a matrix or array.

Syntax

dim(x)
dim(x) <- value

Parameters

Parameter	Type	Default	Description
`x`	any R object	none	An R object such as matrix, data frame, array, or vector
`value`	integer vector	none	A numeric vector specifying the new dimensions

Examples

Getting dimensions of a matrix

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

Getting dimensions of a data frame

# Create a sample data frame
df <- data.frame(
  name = c("Alice", "Bob", "Charlie"),
  age = c(25, 30, 35),
  score = c(85, 92, 78)
)
dim(df)
# [1] 3 3

Setting dimensions on a vector

# Convert a vector into a matrix
vec <- 1:12
dim(vec) <- c(3, 4)
vec
#      [,1] [,2] [,3] [,4]
# [1,]    1    4    7   10
# [2,]    2    5    8   11
# [3,]    3    6    9   12

Checking if an object has dimensions

# Vectors have NULL dimensions
x <- 1:10
dim(x)
# NULL

# Test with is.null()
is.null(dim(x))
# [1] TRUE

Common Patterns

Reshape vectors into matrices: Convert a flat vector into a 2D structure for matrix operations.

Check data frame size: Use dim() to quickly check row and column counts before processing.

Dynamic dimension setting: Create arrays programmatically by assigning dimensions to vectors.