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Re: subscript array question [message #14308 is a reply to message #14302]

Thu, 11 February 1999 00:00

David Ritscher
Messages: 30
Registered: August 1995

Member

> array = intarr(5)
> subs = [0,2,4,4]
> array[subs] = array[subs] + 1
>
> and have the resulting values for array be:
>
> 1 0 1 0 2
>
> Because of the way IDL manages memory for expression evaluation
> and assignments, what happens for the last two elements of the
> addition is that the original value of array[4] is used twice,
> rather than what I want, which is to use the current value of
> array[4] each time. I.e. IDL gives the resulting values for
> array to be:
>
> 1 0 1 0 1
>

With my version, IDL Version 5.1.1, I get the latter, not the former!
I suspect it is true with your version, as well. What IDL does is,
for the duplicate subscript, it does the operation twice, but since
'array' on the right hand of the expression is a copy of the original,
it goes and gets the same '0' twice, incremnts it by '1', and inserts
it into the same location twice.

If in your actual application you're having similar problems, the
uniq function might help you out:

array = intarr(5)
subs = [0,2,4,4]

subs = subs(uniq(subs, sort(subs)))

print, subs
0 2 4

array[subs] = array[subs] + 1

In this case, it gives the same result, as I explained, but in your
application, it might serve to solve your problem.

Good luck,

David Ritscher

--
Cardiac Rhythm Management Laboratory
Department of Medicine
University of Alabama at Birmingham
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Tel: (205) 975-2122 Fax: (205) 975-4720
Email: david.ritscher@bigfoot.com

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[Message index]

		Re: subscript array question By: steinhh on Fri, 12 February 1999 00:00
		Re: subscript array question By: bennetsc on Fri, 12 February 1999 00:00
		Re: subscript array question By: eddie haskell on Thu, 11 February 1999 00:00
		Re: subscript array question By: David Ritscher on Thu, 11 February 1999 00:00

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