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Re: array concatenation [message #62811 is a reply to message #48962]

Fri, 03 October 2008 14:16

lecacheux.alain
Messages: 325
Registered: January 2008

Senior Member

On 3 oct, 17:15, Joost Aan de Brugh <joost...@gmail.com> wrote:
> On Oct 3, 1:19 pm, lecacheux.al...@wanadoo.fr wrote:
>
> 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

Thanks for your reply. I agree with you that such a programming style
is far from ideal.
My point is that it likely can produce some not obvious array boundary
error (and subsequent IDL crash),
while largest used array sizes remain far below the maximum authorized
one.
Or I missed something ?
alx.

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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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