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Re: filling in missing values [message #67859 is a reply to message #67719]

Tue, 25 August 2009 08:50

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

On Aug 25, 8:34 am, Laura <haixia...@gmail.com> wrote:
> Hi, I'm new to IDL and working on data files that assign a particular
> value for where the data is not available. But I want to replace such
> values with the nearest valid value in the array. Is there an
> efficient way to do that instead of loop?

Yes. If you can tolerate always replacing using the good value on the
left, then this would do the trick.

wh = where(data EQ BAD_VALUE, ct)
while ct GT 0 do begin
data[wh] = data[wh-1]
wh = where(data EQ BAD_VALUE, ct)
endwhile

It keeps on replacing until no values are left.

But if you are trying to replace bad values with local good values,
why not use the median function?

medval = median(data, 5) ;; Sliding 5-point median
wh = where(data EQ BAD_VALUE, ct)
if ct GT 0 then data[wh] = medval[wh]

There are ways to be smarter about that. For example the median
includes the bad values, and one may want to filter them out first.

Craig

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[Message index]

		filling in missing values By: Laura on Tue, 25 August 2009 05:34
		Re: filling in missing values By: Laura on Wed, 26 August 2009 08:17
		Re: filling in missing values By: Craig Markwardt on Tue, 25 August 2009 08:50

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