an R object, for example a matrix, array or data frame.

value

For the default method, either NULL or
a numeric vector, which is coerced to integer (by truncation).

Value

For an array (and hence in particular, for a matrix) dim retrieves
the dim attribute of the object. It is NULL or a vector
of mode integer.The replacement method changes the "dim" attribute (provided the
new value is compatible) and removes any "dimnames"and"names" attributes.

dim has a method for data.frames, which returns
the lengths of the row.names attribute of x and
of x (as the numbers of rows and columns respectively).

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
The New S Language.
Wadsworth & Brooks/Cole.

x <- 1:12 ; dim(x) <- c(3,4)
x
# simple versions of nrow and ncol could be defined as followsnrow0 <- function(x) dim(x)[1]
ncol0 <- function(x) dim(x)[2]