Not sure it is "obvious", but this function implements what you describe:
revdim <- function( a, d ) {
dims <- attr( a, "dim" )
idxs <- lapply( seq_along( dims )
, function( dd ) {
if ( d == dd ) seq.int( dims[ dd ], 1, -1 )
else seq.int( dims[ dd ] )
}
)
do.call( `[`, c( list( a ), idxs ) )
}
revdim( junk1, 2 )
On Thu, 1 Jun 2017, Roy Mendelssohn - NOAA Federal wrote:
Hi All:
I have been looking for an elegant way to do the following, but haven't
found it, I have never had a good understanding of any of the "apply"
functions.
A simplified idea is I have an array, say:
junk(5, 10, 3)
where (5, 10, 3) give the dimension sizes, and I want to reverse the
second dimension, so I could do:
junk1 <- junk[, rev(seq_len(10), ]
but what I am after is a general function that will do that where the
array could be two, three or four dimensions, and I pass to the function
which dimension I want to reverse, that is the function can not assume
the number of dimensions of the array nor which dimension to reverse.
For example, if i try:
junk1 <- apply(junk, 2, rev)
junk1 comes out as two-dimensional, not three-dimensional.
It is probably something obvious but I am not getting it.
Thanks for any help.
-Roy
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