R Under development (unstable) (2023-11-16 r85542 ucrt) -- "Unsuffered Consequences"
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> library("R.utils")
Loading required package: R.oo
Loading required package: R.methodsS3
R.methodsS3 v1.8.2 (2022-06-13 22:00:14 UTC) successfully loaded. See ?R.methodsS3 for help.
R.oo v1.25.0 (2022-06-12 02:20:02 UTC) successfully loaded. See ?R.oo for help.

Attaching package: 'R.oo'

The following object is masked from 'package:R.methodsS3':

    throw

The following objects are masked from 'package:methods':

    getClasses, getMethods

The following objects are masked from 'package:base':

    attach, detach, load, save

R.utils v2.12.3 successfully loaded. See ?R.utils for help.

Attaching package: 'R.utils'

The following object is masked from 'package:utils':

    timestamp

The following objects are masked from 'package:base':

    cat, commandArgs, getOption, isOpen, nullfile, parse, warnings

> 
> # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> # Example using an array with a random number of dimensions
> # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> 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")

Array 'x':
> print(x)
   b1 b2 b3
a1  1  4  7
a2  2  5  8
a3  3  6  9
> 
> 
> cat("\nExtract 'x[2:3,...]':\n")

Extract 'x[2:3,...]':
> print(extract(x, "1"=2:3))
   b1 b2 b3
a2  2  5  8
a3  3  6  9
> 
> cat("\nExtract 'x[3,2:3,...]':\n")

Extract 'x[3,2:3,...]':
> print(extract(x, "1"=3,"2"=2:3))
   b2 b3
a3  6  9
> 
> cat("\nExtract 'x[...,2:3]':\n")

Extract 'x[...,2:3]':
> print(extract(x, indices=2:3, dims=length(dim(x))))
   b2
a1  4
a2  5
a3  6
> 
> 
> 
> # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> # Assertions
> # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> 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))
> 
> 
> # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> # Matrix
> # - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> y <- matrix(1:24, nrow=6, ncol=4)
> yA <- y[,2:3]
> yB <- extract(y, indices=list(2:3), dims=length(dim(y)))
> stopifnot(identical(yB, yA))
> 
> proc.time()
   user  system elapsed 
   0.29    0.14    0.40