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avoiding "floating illegal operand" errors with /nan keyword in mean [message #85598]

Tue, 20 August 2013 16:37

Paul Levine
Messages: 29
Registered: February 2008

Junior Member

I have an array with 2800 rows, 2800 columns, and 120 layers, where
each layer is a month from a 10-year time series). I would like to
calculate annual means, so I will end up with an array that is 2800 x
2800 x 10. So

for j = 0, 9 do begin
; make one year subset of 2800x1800x12
subset = array[*,*,j*12:j*12+12]
newarray[0,0,j] = mean(newarray, dimension=3, /nan)
endfor

I am using the /nan keyword because there are a lot of NaNs in the
data. As a result, I get
% Program caused arithmetic error: Floating illegal operand
whenever the mean function tries to calculate an average completely out
of NaN values.

I know that I could just ignore the error, because the results are what
I want them to be, but I'm sure it would be better to figure out how to
prevent the error.

So, I tried the following method of checking to see whether I'm dealing
with all NaNs

for j = 0, 9 do begin
; make one year subset of 2800x1800x12
subset = array[*,*,j*12:j*12+12]
if max(finite(subset)) eq 1 then begin
newarray[0,0,j] = mean(newarray, dimension=3, /nan)
endif else begin
newarray[0,0,j] = make_array(2800,2800,value=!VALUES.D_NAN)
endelse
endfor

This eliminates the error for any situation where the entire subset is
NaN. However, because the mean function is essentially calculating
2800x2800 means of 12 elements each, there are instances where only one
or a few of those 12-element sets are completely NaN, which is not
caught by my method of checking, so I still get the error message.

The only way I can imagine extending my checking method would be to
loop through every row and column of the data set, calculating each
mean one at a time so that I can check whether or not all 12 elements
are NaN. Of course, that would be incredibly inefficient, so I would
not seriously entertain that idea.

Is there a better solution out there, or should I just suck it up and
live with the error message?

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[Message index]

		avoiding "floating illegal operand" errors with /nan keyword in mean By: Paul Levine on Tue, 20 August 2013 16:37
		Re: avoiding "floating illegal operand" errors with /nan keyword in mean By: wlandsman on Tue, 20 August 2013 17:26
		Re: avoiding "floating illegal operand" errors with /nan keyword in mean By: Paul Levine on Tue, 20 August 2013 19:17
		Re: avoiding "floating illegal operand" errors with /nan keyword in mean By: wlandsman on Wed, 21 August 2013 05:58
		Re: avoiding "floating illegal operand" errors with /nan keyword in mean By: Paul Levine on Thu, 22 August 2013 12:16
		Re: avoiding "floating illegal operand" errors with /nan keyword in mean By: Fabzi on Wed, 21 August 2013 14:11
		Re: avoiding "floating illegal operand" errors with /nan keyword in mean By: Paul Levine on Thu, 22 August 2013 12:26

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