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Re: Array element deletion [message #36387 is a reply to message #36386]

Fri, 12 September 2003 06:27

jjbezair
Messages: 2
Registered: July 2003

Junior Member

In article <bjsh0u$q77$1@news.ox.ac.uk>,
Edd Edmondson <eddedmondson@hotmail.com> wrote:
> Supposing I have a big array and I also have an array containing indices
> of unwanted elements. Is there a neat way of removing those elements from
> the array?
>
> Attempts using WHERE() have failed for me* and currently I'm looping
> through the array of indices and deleting them one at a time - which is
> fine when I've only got 20 or 30 of them but I doubt it'll scale well.
>
>
> * - I tried to make a list of indices that I wanted to keep using
> WHERE(indgen(x) ne unwanted) but that only produces the first
> n_elements(unwanted) of the correct indices.
>
> --
> Edd

I'm sure one or more of the gurus here will have a faster solution that
uses histogram, but I've always used index masks for this sort of thing

indexMask = lonarr(n_elements(bigArray))
indexMask(unwanted) = 1
wanted = where(indexMask == 0)
smallArray = bigArray(wanted)

of course you should check that where returns a nonzero array, etc., and
this method uses 4 times the memory of the original array, but memory is
cheap these days, and these 4 lines of code are quick to type...

I'm curious to see what more efficient techniques other people here use.

regards,
Jeff
--

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[Message index]

		Re: Array element deletion By: R.Bauer on Sat, 13 September 2003 10:05
		Re: Array element deletion By: Edd Edmondson on Fri, 12 September 2003 06:44
		Re: Array element deletion By: David Fanning on Fri, 12 September 2003 06:31
		Re: Array element deletion By: jjbezair on Fri, 12 September 2003 06:27
		Re: Array element deletion By: Edd Edmondson on Fri, 12 September 2003 06:19

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