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Re: IDL Way to have a single row/collum act on all rows/collums in an array [message #89542 is a reply to message #89540]

Fri, 24 October 2014 08:11

wlandsman
Messages: 743
Registered: June 2000

Senior Member

On Friday, October 24, 2014 10:32:43 AM UTC-4, JTMHD wrote:
> Hi Guys,
>
>
> What I am trying to do is analogous to the following
>
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
> timedistancearray =FINDGEN(3,3)
>
> timezero = timedistancearray(*,0)
>
> timedistance_minustimezero = FLTARR(3,3)
>
> FOR t=0,2 DO timedistance_minustimezero(*,t)=timedistancearray(*,t)-timez ero
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>
>
> The thing is in this case the array is HUGE so I don't think the FOR loop would be optimum.

1. Looping over 1 dimension is usually fine. The important thing is to do many operations on each iteration, which you are doing in this case.

2. You want to rewrite the equation to avoid use of the asterisk on the left hand side

FOR t=0,2 DO timedistance_minustimezero[0,t]=timedistancearray[*,t]-timez ero

http://www.idlcoyote.com/code_tips/asterisk.html

3. As noted by Russell -- do you need to keep both arrays in memory? If not, then you can write it like this:

FOR t=0,2 DO timedistancearray[0,t]=timedistancearray[*,t]-timezero

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[Message index]

		IDL Way to have a single row/collum act on all rows/collums in an array By: JTMHD on Fri, 24 October 2014 07:32
		Re: IDL Way to have a single row/collum act on all rows/collums in an array By: rryan%stsci.edu on Fri, 24 October 2014 07:49
		Re: IDL Way to have a single row/collum act on all rows/collums in an array By: wlandsman on Fri, 24 October 2014 08:11
		Re: IDL Way to have a single row/collum act on all rows/collums in an array By: JTMHD on Mon, 27 October 2014 05:13

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