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I have a 1d array which is a time series hourly dataset encompassing 49090 points which needs to be converted to netcdf format.

In the code below, result_u2 is a 1d array which stores result from a for loop. It has 49090 datapoints. 

nhours = 49091;#one added to no of datapoints
unout.units = 'hours since 2012-10-20 00:00:00'
unout.calendar = 'gregorian'
ncout = Dataset('output.nc','w','NETCDF3');  
ncout.createDimension('time',nhours); 
datesout = [datetime.datetime(2012,10,20,0,0,0)+n*timedelta(hours=1) for n in range(nhours)]; # create datevalues
timevar = ncout.createVariable('time','float64',('time'));timevar.setncattr('units',unout);timevar[:]=date2num(datesout,unout);
winds = ncout.createVariable('winds','float32',('time',));winds.setncattr('units','m/s');winds[:] = result_u2;
ncout.close()

I'm new to programming. The code I tried above should be able to write the nc file but while running the script no nc file is being created. Please help.

Trishneeta
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1 Answers1

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My suggestions would be to have a look at Python syntax in general, if you want to use it / the netCDF4 package. E.g. there are no semicolons in Python code.

Check out the API documentation - the tutorial you find there basically covers what you're asking. Then, your code could look like 

import datetime
import netCDF4

# using "with" syntax so you don't have to do the cleanup:
with netCDF4.Dataset('output.nc', 'w', format='NETCDF3_CLASSIC') as ncout:
    # create time dimension
    nhours = 49091
    time = ncout.createDimension('time', nhours)

    # create the time variable
    times = ncout.createVariable('time', 'f8', ('time',))
    times.units = 'hours since 2012-10-20 00:00:00'
    times.calendar = 'gregorian'

    # fill time
    dates = [datetime.datetime(2012,10,20,0,0,0)+n*datetime.timedelta(hours=1) for n in range(nhours)]
    times[:] = netCDF4.date2num(dates, units=times.units, calendar=times.calendar)

    # create variable 'wind', dependent on time
    wind = ncout.createVariable('wind', 'f8', ('time',))
    wind.units = 'm/s'
    # fill with data, using your 1d array here:
    wind[:] = result_u2
FObersteiner
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  • I used this entire code and added an ncout.close() at the end. An nc file was created as a result but the command prompt shows a runtime error at this ncout.close(). Can you please tell me why this is happening? – Trishneeta Oct 18 '19 at 04:51
  • Check [the docs](https://docs.python.org/3/whatsnew/2.6.html#pep-343-the-with-statement) on the `with` statement. As I commented in the code, it does the cleanup for you. However, specific to the `netcdf` `Dataset`, it closes the nc id so you can't call `close` again on that id. In contrast, if you invoke a file object by calling `with open(file, ...) as fobj`, you can still call `fobj.close()` and nothing happens. The object reference is still "there", although the contained file pointer is closed already at the end of the `with` statement. – FObersteiner Oct 18 '19 at 06:34
  • More to find on `with` [here](https://stackoverflow.com/questions/3012488/what-is-the-python-with-statement-designed-for?noredirect=1&lq=1) or [there](https://stackoverflow.com/questions/32379147/understanding-the-python-with-statement). and I'm sure there's more. – FObersteiner Oct 18 '19 at 06:47