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Re: Faster way to "shift" array? [message #84787 is a reply to message #84785]

Tue, 11 June 2013 06:04

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

rjp23@le.ac.uk writes:

> I have a longitude array which ranges from 0 to 360 but I want it to range from -180 to 180.
>
> Currently I'm doing this:
> lon=shift(lon, n_elements(lon)/2.)
> lon[where(lon GT 180)]=lon[where(lon GT 180)]-360.
>
> The lon array is 3600 elements and the shift command is taking around 1 second. When multiplied by the thousands of files I need to handle this becomes quite a considerable time component.
>
> Is there a faster way to do this?

I think it is the Where function that is slowing you down. I've always
used the formulas on this page to do the conversion. I've never noticed
them being slow. :-)

http://www.idlcoyote.com/map_tips/lonconvert.html

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thue. ("Perhaps thou speakest truth.")

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[Message index]

		Faster way to "shift" array? By: rjp23 on Tue, 11 June 2013 05:50
		Re: Faster way to "shift" array? By: rjp23 on Tue, 11 June 2013 05:52
		Re: Faster way to "shift" array? By: David Fanning on Tue, 11 June 2013 06:04
		Re: Faster way to "shift" array? By: rjp23 on Tue, 11 June 2013 06:23
		Re: Faster way to "shift" array? By: David Fanning on Tue, 11 June 2013 06:28
		Re: Faster way to "shift" array? By: David Fanning on Tue, 11 June 2013 06:35
		Re: Faster way to "shift" array? By: rjp23 on Tue, 11 June 2013 06:44
		Re: Faster way to "shift" array? By: Fabzi on Tue, 11 June 2013 09:33
		Re: Faster way to "shift" array? By: David Fanning on Tue, 11 June 2013 10:23
		Re: Faster way to "shift" array? By: Yngvar Larsen on Tue, 11 June 2013 14:39

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