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Re: What are the rules for automatic removal of singleton dimensions, and can I have a way of disabling them, please? [message #82549]

Sun, 23 December 2012 20:25

Jeremy Bailin
Messages: 618
Registered: April 2008

Senior Member

On 12/23/12 6:01 PM, Tom Grydeland wrote:
> Hello all,
>
> I was trying to visualize subsections of a windowing function when this bit me.
>
> I was creating piecewise results in an array res[ix, iy, ii, jj], where the partial results were sums up to some value in the final two indices
>
> for ii = 0, Kx-1 do begin
> for jj = 0, Ky-1 do begin
> visualize, total(total(res[*,*,0:ii,0:jj], 4), 3)
> endfor
> endfor
>
> but the problem is that IDL (arbitrarily, IMO) discards trailing singleton dimensions on my indexing, so that res[*,*,0:ii,0:jj] ends up as a two-dimensional array when both ii and jj are zero, and a three-dimensional index on subsequent cases of jj being zero, which again causes the calls to 'total' to fail. The innermost portion of these loops become extraordinarily messy if trying to fix this problem.
>
> I've fixed my program by reordering the indices (to [ii, jj, ix, iy]), but I am still miffed that this should be necessary.
>
> Similarly, when I concatenate arrays of dimensions [x, j] and [y, j], I expect a result with dimensions [x+y, j], even when j is equal to 1. I'm trying to write programs independent of the actual value of j, but these arbitrary removals of singleton dimensions make my task that much harder.
>
> Is there a way to disable this stripping of singleton dimensions?
>
> --Tom Grydeland
>

I would give my full support to having a compile_opt to do this
(Chris?)... as David says, there's no way in hell that's ever going to
be the default behaviour, but I would kill to not have to worry about
these cases in some of my more dimension-juggling code!

-Jeremy.

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		Re: What are the rules for automatic removal of singleton dimensions, and can I have a way of disabling them, please? By: Jeremy Bailin on Sun, 23 December 2012 20:25
		Re: What are the rules for automatic removal of singleton dimensions, and can I have a way of disabling them, please? By: David Fanning on Sun, 23 December 2012 15:37
		Re: What are the rules for automatic removal of singleton dimensions, and can I have a way of disabling them, please? By: tom.grydeland on Tue, 25 December 2012 15:45

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