asub | R Documentation |
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, ...)
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 |
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
|
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.
A subset of x
, as returned by x[...]
.
Tony Plate tplate@acm.org
~put references to the literature/web site here ~
Extract
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)
asub(x, list(1:2,3:4), c(1,3))
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