Arbitrary subsetting of array-like objects at specified indices

Subset array-like objects at specified indices. asub() is a S3 generic, with one method, asub.default, supplied in the abind package.

asub(x, idx, dims = seq(length.out = max(length(dim(x)), 1)), drop = NULL, ...)

Arguments

x: The object to index
idx: A list of indices (e.g., a list of a mixture of integer, character, and logical vectors, but can actually be anything). Can be just a vector in the case that length(dims)==1. NULL entries in the list will be treated as empty indices.
dims: The dimensions on which to index (a numeric or integer vector). The default is all of the dimensions.
drop: The 'drop' argument to index with (the default is to not supply a 'drop' argument
...: There are no additional arguments allowed for asub.default but other methods may use them.

Details

Constructs and evaluates an expression to do the requested indexing. E.g., for x with length(dim(x))==4 the call asub(x, list(c("a","b"), 3:5), 2:3) will construct and evaluate the expression x[, c("a","b"), 3:5, ], and the call asub(x, 1, 2, drop=FALSE) will construct and evaluate the expression x[, 1, , , drop=FALSE].

asub checks that the elements of dims are in the range 1 to length(dim(x)) (in the case that x is a vector, length(x) is used for dim(x)). Other than that, no checks are made on the suitability of components of idx as indices for x. If the components of idx have any out-of-range values or unsuitable types, this will be left to the subsetting method for x to catch.

Value

A subset of x, as returned by x[...].

References

~put references to the literature/web site here ~

Author

Tony Plate tplate@acm.org

Examples

x <- array(1:24,dim=c(2,3,4),dimnames=list(letters[1:2],LETTERS[1:3],letters[23:26]))
asub(x, 1, 1, drop=FALSE)
#> , , w
#> 
#>   A B C
#> a 1 3 5
#> 
#> , , x
#> 
#>   A B  C
#> a 7 9 11
#> 
#> , , y
#> 
#>    A  B  C
#> a 13 15 17
#> 
#> , , z
#> 
#>    A  B  C
#> a 19 21 23
#> 
asub(x, list(1:2,3:4), c(1,3))
#> , , y
#> 
#>    A  B  C
#> a 13 15 17
#> b 14 16 18
#> 
#> , , z
#> 
#>    A  B  C
#> a 19 21 23
#> b 20 22 24
#>