[Bug]: xarray.open_mfdataset drops .encoding attributes, need to handle with xcdat.open_mfdataset()

[tomvothecoder]

What happened?

Related to #302 (comment).

Nice catch! I found an open xarray issue related to xr.open_mfdataset() dropping encoding attributes.

• save "encoding" when using open_mfdataset pydata/xarray#2436
• save "encoding" when using open_mfdataset pydata/xarray#2436 (comment)

Somebody mentions this about the issue here pydata/xarray#2436 (comment):

However, there is another problem related to xarray.open_mfdataset:
The encoding dictionary gets lost somewhere during the merging operation of the datasets of the respective files (https://github.com/pydata/xarray/issues/2436).

This leads to problems for example with cf-xarray when trying to detect coordinates or bounds, but also leads to problems related to the time axis encoding apparently (as seen in the linked issue). I managed at least to avoid the problems for cf-xarray bounds and coordinates detection by using the decode functionality of xarray only after the datasets have been read in (leaving however the unnecessary time dimension in place ...):

ds = xarray.open_mfdataset("/path/to/files/*.nc")
ds = xarray.decode_cf(ds, decode_coords="all")

I think we might need to use the preprocess function to save the .encoding dict, or some other workaround like from one of the comments.

The temporal averaging APIs require decoded time coordinates and the ds.time.encoding dict to be populated with the "calendar" attr.

What did you expect to happen?

The .encoding attributes should remain persistent after running xcdat.open_mfdataset().

This does not affect xcdat.open_dataset().

Minimal Complete Verifiable Example

>> import xcdat

>> ds = xcdat.open_mfdataset(
    "/p/css03/cmip5_css02/data/cmip5/output1/ICHEC/EC-EARTH/historical/mon/atmos/Amon/r1i1p1/tas/1/*.nc")

>> ds.time.encoding

{}

Relevant log output

No response

Anything else we need to know?

Possible Solutions

1. Store .encoding and copy it back to the final merged dataset (maybe with preprocess kwarg)

• save "encoding" when using open_mfdataset pydata/xarray#2436 (comment)

Related Issues

Environment

xcdat 0.3.0

INSTALLED VERSIONS

commit: None
python: 3.9.13 | packaged by conda-forge | (main, May 27 2022, 16:56:21)
[GCC 10.3.0]
python-bits: 64
OS: Linux
OS-release: 3.10.0-1160.45.1.el7.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: ('en_US', 'UTF-8')
libhdf5: 1.12.1
libnetcdf: 4.8.1

xarray: 2022.3.0
pandas: 1.4.3
numpy: 1.22.4
scipy: 1.9.0
netCDF4: 1.5.8
pydap: None
h5netcdf: None
h5py: None
Nio: None
zarr: None
cftime: 1.6.0
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: None
dask: 2022.6.1
distributed: 2022.6.1
matplotlib: 3.5.2
cartopy: None
seaborn: None
numbagg: None
fsspec: 2022.7.1
cupy: None
pint: None
sparse: 0.13.0
setuptools: 63.3.0
pip: 22.1.2
conda: None
pytest: 7.1.2
IPython: 8.4.0
sphinx: 4.5.0