# How to make a sum in NetCDF4 by xarray

#### Tags: netcdf, netcdf4, pandas, python, python-xarray

I would like to make a monthly sums of my NetCDF4 file from daily values for precipitation. However, I am quite not sure what I am doing wrong. It seems that something has changed from the code in this post: Sum a daily time series into a monthly time series with a NaN value threshold

I didn’t find anything helpful in the library documentation.

Here is my code:

import netCDF4
from netCDF4 import Dataset
import numpy as np
import xarray as xr
import pandas as pd

data = xr.open_dataset('C3S_concat_cropped.nc')
# or I can use
data2 = Dataset("C3S_concat_cropped.nc", "r", format="NETCDF4")
print(data)
Out:
<xarray.Dataset>
Dimensions:             (lat: 115, lon: 140, time: 15157)
Coordinates:
* lat                 (lat) float64 -7.4 -7.5 -7.6 -7.7 ... -18.6 -18.7 -18.8
* lon                 (lon) float64 21.1 21.2 21.3 21.4 ... 34.8 34.9 35.0
* time                (time) datetime64[ns] 1979-01-01 ... 2020-06-30
Data variables:
Precipitation_Flux  (time, lat, lon) float32 ...

daily_dataset = xr.Dataset({'Precipitation_Flux': (['time', 'lat', 'lon'],
data['Precipitation_Flux'][:, :, :])}, coords={'lat': (data['lat'][:]),
'lon': (data['lon'][:]), 'time': pd.date_range('1979-01-01', periods=15157)})

monthly_dataset = daily_dataset['Precipitation_Flux'].resample(indexer='M', time="1D",
skipna=False).sum()

My ValueError:

ValueError: the first argument to .resample must be a dictionary