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array indices again [message #15631]

Thu, 03 June 1999 00:00

Henry Chapman
Messages: 10
Registered: February 1997

Junior Member

Hi all,

I remember a few weeks back there was a lot of discussion about indexing
multiple dimensions of arrays, and doing things such as

IDL> print,(a[x,*])[*,x]

I just noticed something that may or may not have come up in those
discussions (but I wasn't paying attention). It is most easily
explained by Liam's example of extracting every second row and column of
an array

IDL> a=indgen(10,10)
IDL> x=indgen(5)*2
IDL> print, a[x, x, 0]
0 2 4 6 8
20 22 24 26 28
40 42 44 46 48
60 62 64 66 68
80 82 84 86 88

It seems that by extending the 2-d array a into another dimension, where
the extra dimension has no size (sounds like string theory!) the
indexing works the way I want it to. I noticed this when I had a 3-d
array and was extracting a 2-d array from it, as in b[x, x, i] where x
is a 1-d array and i is a scalar. This seems to work on arrays of any
dimension.

I apologise if this was mentioned before,

Henry.

--
Henry Chapman mailto:chapman9@llnl.gov
Information Science & Technology Program
Lawrence Livermore National Lab
L-395, 7000 East Ave., Livermore CA 94550

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[Message index]

		array indices again By: Henry Chapman on Thu, 03 June 1999 00:00
		Re: array indices again By: Martin Schultz on Thu, 03 June 1999 00:00

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