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Re: Loop Arrays [message #27110 is a reply to message #26977]

Tue, 09 October 2001 15:06

Ken Mankoff
Messages: 158
Registered: February 2000

Senior Member

On Tue, 9 Oct 2001, Mark Hadfield wrote:

> From: "Ken Mankoff" <mankoff@lasp.colorado.edu>
>> I am interested in creating circular arrays, where subscripts that would
>> be out-of-bounds on a regular array just start indexing on the other side
>> of the array.
>
> You can do quite a lot with ordinary arrays using arrays of indices, eg
>
> a = indgen(10)
> print, a[ [0,10,20,100] mod n_elements(a)]
>

This is the technique I have been using. However there are 2 cases it does
not cover:

1) negative indexes require a few more lines of code to get your example
to work. I would recode it as:

a = indgen( 10 )
indexes = [ 0,10,20,100,-10,-22 ] ;;; or some other values...
ind = indexes mod n_elements( a )
neg = where( ind lt 0, num )
if ( num ne 0 ) then ind[ neg ] = ind[ neg ] + n_elements( a )
print, a[ ind ]

2) subscript ranges. You cannot do:
print, a[ 8:12 mod n_elements(a) ]

It is these two specific abilities that I would like to have.

-k.

--
Ken Mankoff
LASP://303.492.3264
http://lasp.colorado.edu/~mankoff/

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[Message index]

		Re: Loop Arrays By: Mark Hadfield on Tue, 09 October 2001 12:59
		Re: Loop Arrays By: David Fanning on Tue, 09 October 2001 12:57
		Re: Loop Arrays By: Ken Mankoff on Tue, 09 October 2001 15:06
		Re: Loop Arrays By: Martin Downing on Mon, 15 October 2001 14:43
		Re: Loop Arrays By: Ken Mankoff on Mon, 15 October 2001 09:35

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