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Re: array concatenation [message #62815 is a reply to message #48962]

Fri, 03 October 2008 08:15

Joost Aan de Brugh
Messages: 16
Registered: July 2008

Junior Member

On Oct 3, 1:19 pm, lecacheux.al...@wanadoo.fr wrote:
> On 3 oct, 13:12, lecacheux.al...@wanadoo.fr wrote:
> I got a strange error when using the array concatenation construct
> within a large loop (a few thousands).
> something like:
> b = 0B
> for i=0,999 do begin
> ... compute a = array of bytes (a few 100) ...
> b = [b, a]
> endfor
> This could crash IDL and even, randomly, crash the system (Win2K).
> Nothing found by catching errors.
> Is there some limits in the implicit addressing of such arrays ?
> The error disappeared when compiling with COMPILE_OPT IDL2.

Hello,

Maybe it has something to do with the array descriptor. Anyway, in a
large group concatenation is not the most elegant way. In Matlab (a
language similar to IDL), you get a warning if you use such a
construction. It has to do with the fact that if your array grows, you
ask your system for more space. A safer way is to ask for enough space
at once.

afh = a few 100

b = BytArr(afh*1000) ; Here is where you ask for a lot of space.
for i=0,999 do begin
... compute a = array of bytes (a few 100) ...
b[i*afh:(i+1)*afh-1] = a ; Now b does not grow in the loop
end

Or use a 2D array

b = BytArr(afh,1000) ; Here, you ask for the space again.
for i=0,999 do begin
... compute a = array of bytes (a few 100) ...
b[*,i] = a ; Now b does not grow in the loop
end

Cheers,
Joost

b = Reform(b,afh*1000) ; Or b = Reform(b,N_Elements(b))

It is a bit harder if you have different 'a few 100's for each
iteration

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[Message index]

		Array concatenation By: maye on Wed, 07 June 2006 03:41
		Re: Array concatenation By: Vince Hradil on Tue, 17 July 2007 09:25
		Re: Array concatenation By: Julio[1] on Tue, 17 July 2007 06:40
		Re: Array concatenation By: Conor on Tue, 17 July 2007 05:11
		Re: Array concatenation By: Paolo Grigis on Tue, 17 July 2007 00:28
		Re: Array concatenation By: Peter Clinch on Tue, 17 July 2007 00:24
		Re: array concatenation By: Wox on Thu, 31 January 2008 00:43
		Re: array concatenation By: Spon on Wed, 30 January 2008 08:38
		Re: array concatenation By: Allan Whiteford on Wed, 30 January 2008 08:21
		Re: array concatenation By: Karl[1] on Fri, 03 October 2008 18:11
		Re: array concatenation By: David Fanning on Fri, 03 October 2008 14:20
		Re: array concatenation By: lecacheux.alain on Fri, 03 October 2008 14:16
		Re: array concatenation By: Joost Aan de Brugh on Fri, 03 October 2008 08:15
		Re: array concatenation By: lecacheux.alain on Fri, 03 October 2008 04:19

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