Re: Treating -999 values in ASCII as missing

[Francesco Potortì]

>I have some data stored in ASCII files which I use 'load' command to read.
>In those files, missing values are stored as -999.
>
>I would like to know how do I say to Octave, at read time, that those -999
>values must be treated as missing values.
>
>Is there a simple function to do this?
>
>I've searched this, but found nothing. The best I can think is to span all
>the data with a for-loop, checking every matrix element and replacing it
>when was the case.

If you have a matrix A and want to replace all -999 values with
something else (say, 0), you do:

 A(A==-999) = 0

For doing statistical computations, you can use NA as a placeholder for
missing values.  To compute the mean of a vector V ignoring NA values,
you do

 nanmean(A)

This ignores all NaN values, and NA is a particular NaN values, so it
is ignored.  There are some other functions that ignore NaN values,
specifically nanmax, nanmedian, nanmin, nanstd, nansum, nanvar.

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