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Re: make all array values equal to zero [message #89863 is a reply to message #89862]

Thu, 11 December 2014 09:52

Michael Galloy
Messages: 1114
Registered: April 2006

Senior Member

On 12/11/14, 9:59 AM, alx wrote:
> IDL> A=randomn(rien,10000000)
> IDL> tic & A *= (A gt 1) & toc
> % Time elapsed: 0.078000069 seconds.
> IDL> tic & A[where(A gt 1,/NULL)]=0 & toc
> % Time elapsed: 0.047000170 seconds.
>
> The "where" solution appears to be somewhat faster.

Your solution should scale with the number of elements which match the
condition.

So for 50% of the elements matching:

IDL> n = 10000000L
IDL> a = 2.0 * randomu(seed, n)
IDL> tic & a *= (A gt 1) & toc
Elapsed Time: 0.024550
IDL> a = 2.0 * randomu(seed, n)
IDL> tic & A[where(A gt 1,/NULL)]=0 & toc
Elapsed Time: 0.023005

For about 15% of the elements matching:

IDL> a = randomn(seed, n)
IDL> tic & A[where(A gt 1,/NULL)]=0 & toc
Elapsed Time: 0.014616

For all of the elements matching:

IDL> a = randomu(seed, n) + 1.0
IDL> tic & A[where(A gt 1,/NULL)]=0 & toc
Elapsed Time: 0.024564

But, in any case, the WHERE solution seems equal or faster in all cases.

Mike
--
Michael Galloy
www.michaelgalloy.com
Modern IDL: A Guide to IDL Programming (http://modernidl.idldev.com)
Research Mathematician
Tech-X Corporation

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[Message index]

		make all array values equal to zero By: g.nacarts on Thu, 11 December 2014 07:12
		Re: make all array values equal to zero By: lecacheux.alain on Thu, 11 December 2014 07:20
		Re: make all array values equal to zero By: Helder Marchetto on Thu, 11 December 2014 07:20
		Re: make all array values equal to zero By: Michael Galloy on Thu, 11 December 2014 07:58
		Re: make all array values equal to zero By: lecacheux.alain on Thu, 11 December 2014 08:59
		Re: make all array values equal to zero By: Michael Galloy on Thu, 11 December 2014 09:52
		Re: make all array values equal to zero By: g.nacarts on Fri, 12 December 2014 06:54

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