Drop Redundant Extent Information

Description

Delete the dimensions of an array which have only one level.

Usage

drop(x)

Arguments

Value

If x is an object with a dim attribute (e.g., a matrix or array), then drop returns an object like x, but with any extents of length one removed. Any accompanying dimnames attribute is adjusted and returned with x: if the result is a vector the names are taken from the dimnames (if any). However, if the result is a vector of length one, then it does not get names unless exactly one component of the dimnames is non-NULL, in which case that component is used.

Array subsetting ([) performs this reduction unless used with drop = FALSE, but sometimes it is useful to invoke drop directly.

See Also

drop1 which is used for dropping terms in models, and droplevels used for dropping unused levels from a factor.

Examples

dim(drop(array(1:12, dim = c(1,3,1,1,2,1,2)))) # = 3 2 2
drop(1:3 %*% 2:4)  # scalar product - w/o drop(.), would return 1x1 matrix

# Behavior when result is length-1 vector:
(x <- x1 <- x2 <- array(0, c(1L, 1L), list("a", "b")))
colnames(x1) <- rownames(x2) <- NULL
names(drop(x )) # NULL
names(drop(x1)) #  "a"
names(drop(x2)) #  "b"