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Set zeros to NaN (or equivalent)

Added by Holly Ayres about 5 years ago

Hello,

I was wondering if there was a way to set zero values to NaN or equivalent (missing data?) using CDO. I need to do this for -ymonmean averaging of sea ice, so it does not include grid boxes/years that do not have any sea ice in? I would normally do this on Matlab but my output netcdf files are causing problems further on, so I figured it's worth a try in CDO as these output files I have got working.

Thank you,
Holly


Replies (5)

RE: Set zeros to NaN (or equivalent) - Added by Holly Ayres about 5 years ago

Or, possibly a way to average just ignoring zeros? A bit of a long shot.

Thank you,
Holly

RE: Set zeros to NaN (or equivalent) - Added by Ralf Mueller about 5 years ago

hi!

Set a constant value (here zero) to missing value with

cdo -setctomiss,0
Check "here:https://code.mpimet.mpg.de/projects/cdo/embedded/index.html#x1-310001.7 for how missing values are handled by CDO

hth + merry Xmas
ralf

RE: Set zeros to NaN (or equivalent) - Added by Ralf Mueller about 5 years ago

ah, in case you don't know: the term missing value is part of the netcdf standard. it is used for a certain numeric value, which indicates that the data at this point is missing. _FillValue is an equivalent term for this (https://www.unidata.ucar.edu/software/netcdf/docs/fill_values.html).

Avoid NaN whenever you can, because different tools might handle this in different ways whereas the stuff above is part of the standard.

cheers
ralf

RE: Set zeros to NaN (or equivalent) - Added by Holly Ayres about 5 years ago

Thank you for this, very helpful!

Is there a way to just do a -ymonmean and not include zeros? Cut out the middle man so to speak.

Thank you,
Holly

RE: Set zeros to NaN (or equivalent) - Added by Ralf Mueller about 5 years ago

as i said: you can set them to missing values and they will be ignored

cdo -yearmonmean -setctomiss,0 <input> <output>

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