Drop dimensions of an array object

Drop degenerate dimensions of an array object. Offers less automaticity and more control than the base drop() function. adrop() is a S3 generic, with one method, adrop.default, supplied in the abind package.

adrop(x, drop = TRUE, named.vector = TRUE, one.d.array = FALSE, ...)

Arguments

x

An array (including a matrix)

drop

A logical or numeric vector describing exactly which dimensions to drop. It is intended that this argument be supplied always. The default is very rarely useful (drop=TRUE means drop the first dimension of a 1-d array).

named.vector

Optional, defaults to TRUE. Controls whether a vector result has names derived from the dimnames of x.

one.d.array

Optional, defaults to FALSE. If TRUE, a one-dimensional array result will be an object with a dim attribute of length 1, and possibly a dimnames attribute. If FALSE, a one-dimensional result will be a vector object (named if named.vector==TRUE).

...

There are no additional arguments allowed for adrop.default but other methods may use them.

Details

Dimensions can only be dropped if their extent is one, i.e., dimension i of array x can be dropped only if dim(x)[i]==1. It is an error to request adrop to drop a dimension whose extent is not 1.

A 1-d array can be converted to a named vector by supplying drop=NULL (which means drop no dimensions, and return a 1-d array result as a named vector).

Value

If x is an object with a dim attribute (e.g., a matrix or array), then adrop returns an object like x, but with the requested extents of length one removed. Any accompanying dimnames attribute is adjusted and returned with x.

Author

Tony Plate tplate@acm.org

See also

abind

Examples

x <- array(1:24,dim=c(2,3,4),dimnames=list(letters[1:2],LETTERS[1:3],letters[23:26]))
adrop(x[1,,,drop=FALSE],drop=1)
#>   w  x  y  z
#> A 1  7 13 19
#> B 3  9 15 21
#> C 5 11 17 23
adrop(x[,1,,drop=FALSE],drop=2)
#>   w x  y  z
#> a 1 7 13 19
#> b 2 8 14 20
adrop(x[,,1,drop=FALSE],drop=3)
#>   A B C
#> a 1 3 5
#> b 2 4 6
adrop(x[1,1,1,drop=FALSE],drop=1)
#>   w
#> A 1
adrop(x[1,1,1,drop=FALSE],drop=2)
#>   w
#> a 1
adrop(x[1,1,1,drop=FALSE],drop=3)
#>   A
#> a 1
adrop(x[1,1,1,drop=FALSE],drop=1:2)
#> w 
#> 1 
adrop(x[1,1,1,drop=FALSE],drop=1:2,one.d=TRUE)
#> w 
#> 1 
adrop(x[1,1,1,drop=FALSE],drop=1:2,named=FALSE)
#> [1] 1
dim(adrop(x[1,1,1,drop=FALSE],drop=1:2,one.d=TRUE))
#> [1] 1
dimnames(adrop(x[1,1,1,drop=FALSE],drop=1:2,one.d=TRUE))
#> [[1]]
#> [1] "w"
#> 
names(adrop(x[1,1,1,drop=FALSE],drop=1:2,one.d=TRUE))
#> [1] "w"
dim(adrop(x[1,1,1,drop=FALSE],drop=1:2))
#> NULL
dimnames(adrop(x[1,1,1,drop=FALSE],drop=1:2))
#> NULL
names(adrop(x[1,1,1,drop=FALSE],drop=1:2))
#> [1] "w"