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Re: Odd behaviour in array indexing ? [message #34185 is a reply to message #34182]

Fri, 21 February 2003 07:40

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

mwvogel (mvogel@rdiag.fgg.eur.nl) writes:

> Today I realized something is amiss in IDL
> When I do
> index = [1,0,2,3,1,2,3,4]
> m = FLTARR(8)
> d = FINDGEN(8)
> m[index] = d
> print, m
> 1.00000 4.00000 5.00000 6.00000 7.00000
> 0.000000 0.000000 0.000000
>
> Now I would have assumed that IDL would automatically *add* the numbers with
> identical indices. Not doing
> so is a potential performance penaly, right ? Or am I mistaken....

I find it hard to say what exactly you are trying to
do here, but IDL seems to be working exactly as I would
expect it to. Variables on the left hand side of the
expression are having things assigned to them. I'm not
sure why you think the assignments should *add*. If I do
this:

a = intarr(2)
a[1] = 5

And later,

a[1] = 6

I sure don't want a[1] to equal 11. That is exactly
what you seem to be asking for above.

Cheers,

David

--

David W. Fanning, Ph.D.
Fanning Software Consulting, Inc.
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155

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[Message index]

		Re: Odd behaviour in array indexing ? By: Liam E. Gumley on Fri, 21 February 2003 09:29
		Re: Odd behaviour in array indexing ? By: James Kuyper on Fri, 21 February 2003 07:48
		Re: Odd behaviour in array indexing ? By: tam on Fri, 21 February 2003 07:53
		Re: Odd behaviour in array indexing ? By: David Fanning on Fri, 21 February 2003 07:40

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