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Re: 2 arrays, average, missing data [message #45414 is a reply to message #45413]

Thu, 08 September 2005 07:55

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

"KJM" <kimberlite@gmail.com> writes:
> HI All,
> 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).

Here's something without WHERE's

MISSING = 0.0
C = (A+B)/((A NE MISSING) + (B NE MISSING))

You'll get NaN whereever both values are missing. This is easily
extendible to the case where you have N arrays with M values each.
Just arrange them into an MxN array,

DATA = DBLARR(M,N)
... fill data values ...
C = TOTAL(DATA,2)/TOTAL(DATA NE MISSING,2)

Craig

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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@REMOVEcow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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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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