CODEWITHSUNDEEP
pythonnetcdf
hpnk85
hpnk85

Reputation: 395

How to unmask netcdf in Python

I am opening a NetCDF file in Python, as a file object. However, when I want to check the data and put the variables in a list, it shows that the values are masked! How do I unmask them?

The code I have is:

file = 'C:/Users/cru/0.5x0.5/pre/cru_ts3.23.2001.2010_.pre.dat.nc'
fileobj = netCDF4.Dataset(file)

tsvar = fileobj.variables[varname]
dec_list = []
dec_list.append(numpy.mean(tsvar[12,25,35]))
print dec_list

tsvar shape is: (120, 360, 720) #(month, lat,lon)

The output of printing dec_list is: [masked]. I see the same result for any month, lat or lon.

Upvotes: 1

Views: 3970

Answers (2)

Eric Bridger
Eric Bridger

Reputation: 3794

Read about numpy masked arrays numpy.ma

if type(tsvar) ==  <class 'numpy.ma.core.MaskedArray'>

You can use numpy.ma.mean():

#instead of this numpy.mean(tsvar[12,25,35]) # try numpy.ma.mean(tsvar[12,25,35])

Upvotes: 1

bearjoejoe
bearjoejoe

Reputation: 11

netCDF4 load the data to masked array of numpy in default. The masked element is considered to be invalid for the data processing. Here is a good link for explanation: https://currents.soest.hawaii.edu/ocn760_4/_static/masked_arrays.html

Masked array may have different sum, mean and variance, you can check there is masked value in your array by:

print(np.where(tsvar.mask==True))

If you want to change the default set of loading in masked array, you can turn the mask operation off by:

for k in fileobj.variables:
      fileobj.variables[k].set_auto_mask(False)

Upvotes: 1

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