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Re: 2 arrays, average, missing data [message #45417 is a reply to message #45415]

Thu, 08 September 2005 07:38

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

KJM writes:

> IDL newbie here, I would appreciate any help. (Have been pouring over
> Gumley and Fanning books for a day now, can't get this simple
> calculation done.)
>
> I have 2 arrays. Each array has float values and missing
> data(value=0). I want to create a third array that has the average of
> the two arrays if there are two good values. Otherwise, I want the
> third array to take the value of the array that has data.
>
>
> If my arrays are A and B, and the new array C, I know I can use:
>
> C = (A+B)/2
>
> to get the third array with averaged values. The only problem, is
> that missing data values are averaged in with good values also. (ie:
> 275 averaged w/ 0 -- when I want to just take the 275 value).
>
> Have tried If statements, -- but I realize these are all for scalar
> values, not array.
>
> My basic idea is:
>
> If A = 0, C = B
> If B = 0, C = A
> If A and B EQ 0, C = 0
> If A and B NE 0, C = (A+B)/2

I think your basic idea is great. :-)

Here is what I would do.

C = (A + B) / 2
indices = WHERE(A EQ 0 AND B NE 0, count)
IF count GT 0 THEN C[indices] = B
indices = WHERE(A NE 0 AND B EQ 0, count)
IF count GT 0 THEN C[indices] = A

Cheers,

David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/

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[Message index]

		Re: 2 arrays, average, missing data By: James Kuyper on Thu, 08 September 2005 10:31
		Re: 2 arrays, average, missing data By: kimberlite on Thu, 08 September 2005 08:46
		Re: 2 arrays, average, missing data By: Benjamin Luethi on Thu, 08 September 2005 08:24
		Re: 2 arrays, average, missing data By: Craig Markwardt on Thu, 08 September 2005 07:55
		Re: 2 arrays, average, missing data By: R.G. Stockwell on Thu, 08 September 2005 07:53
		Re: 2 arrays, average, missing data By: David Fanning on Thu, 08 September 2005 07:38

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