R.utils (version 2.3.0)

extract.array: Extract a subset of an array, matrix or a vector with unknown dimensions

Description

Extract a subset of an array, matrix or a vector with unknown dimensions.

This method is useful when you do not know the number of dimensions of the object your wish to extract values from, cf. example.

Usage

"extract"(x, ..., indices=list(...), dims=names(indices), drop=FALSE)

Arguments

x

An array or a matrix.

...

These arguments are by default put into the indices list.

indices

A list of index vectors to be extracted.

dims

An vector of dimensions - one per element in indices - which will be coerced to integers. If NULL, it will default to seq_along(indices).

drop

If TRUE, dimensions of length one are dropped, otherwise not.

Value

Returns an array.

See Also

slice.index()

Examples

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# Example using an array with a random number of dimensions
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maxdim <- 4
dim <- sample(3:maxdim, size=sample(2:maxdim, size=1), replace=TRUE)
ndim <- length(dim)
dimnames <- list()
for (kk in 1:ndim)
  dimnames[[kk]] <- sprintf("%s%d", letters[kk], 1:dim[kk])
x <- 1:prod(dim)
x <- array(x, dim=dim, dimnames=dimnames)

cat("\nArray 'x':\n")
print(x)


cat("\nExtract 'x[2:3,...]':\n")
print(extract(x, "1"=2:3))

cat("\nExtract 'x[3,2:3,...]':\n")
print(extract(x, "1"=3,"2"=2:3))

cat("\nExtract 'x[...,2:3]':\n")
print(extract(x, indices=2:3, dims=length(dim(x))))



# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# Assertions
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y <- array(1:24, dim=c(2,3,4))
yA <- y[,,2:3]
yB <- extract(y, indices=list(2:3), dims=length(dim(y)))
stopifnot(identical(yB, yA))

yA <- y[,2:3,2]
yB <- extract(y, indices=list(2:3,2), dims=c(2,3), drop=TRUE)
stopifnot(identical(yB, yA))