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Re: Array concatenation [message #48961 is a reply to message #42493]

Wed, 07 June 2006 06:41

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

maye writes:

> I was searching for an effective way to do this, but can't find anybody
> writing about what (as usual) seems to be an obvious problem/task to
> me. :)
> I don't know how many elements I will collect while scanning a bunch of
> images, so I want to use array concatenation to collect the values like
> this:
> means = [means, currMean]
> But for this to compile/run properly, I need mean to exist before.
> If I do a
> means = 0.
> before the loop, I will always have a zero-element in the beginning
> that I don't want at plotting time. Of course I could remove it with
> means = means[1:*]
> but not only does this waste resources, it also becomes cumbersome if I
> collect 20 different data values, for that I ALL have to remove the
> first value?
> Surely there must be a better way?
> Please help me to program IDL efficiently! :)

I think most people do something like this:

IF N_Elements(means) EQ 0 THEN means = [currMean] ELSE $
means = [Temporary(means), currMean]

Or, did you mean something that doesn't involve any coding? :-)

Be aware that if your loop is large, it is much more
efficient to allocate the memory for your array in chucks
of say 100 or 1000, and then fill it up, then it is to
continuously re-define your array like this.

Cheers,

David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/

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[Message index]

		Array Concatenation Optimization By: KM on Tue, 08 February 2005 11:19
		Re: Array concatenation By: FL on Wed, 07 June 2006 09:12
		Re: Array concatenation By: Michael Galloy on Wed, 07 June 2006 08:06
		Re: Array concatenation By: David Fanning on Wed, 07 June 2006 07:33
		Re: Array concatenation By: Paul Van Delst[1] on Wed, 07 June 2006 07:21
		Re: Array concatenation By: David Fanning on Wed, 07 June 2006 06:41

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