id,node_id,number,title,user,state,locked,assignee,milestone,comments,created_at,updated_at,closed_at,author_association,active_lock_reason,draft,pull_request,body,reactions,performed_via_github_app,state_reason,repo,type
1933496257,I_kwDOAMm_X85zPs_B,8288,New library for handling complex numbers in netCDF,1486942,closed,0,,,7,2023-10-09T17:21:20Z,2024-03-25T13:16:40Z,2024-03-25T13:16:40Z,CONTRIBUTOR,,,,"### Is your feature request related to a problem?

Complex numbers are not natively handled by netCDF, and currently only the `h5netcdf` engine in xarray can handle them. However, it produces files unreadable by current versions of netCDF. There are also [many different conventions](https://github.com/PlasmaFAIR/nc-complex/blob/main/README.md#conventions-for-complex-numbers), and `h5netcdf` can only read a few of them.

### Describe the solution you'd like

I've written a [drop-in extension to netCDF](https://github.com/PlasmaFAIR/nc-complex) that seamlessly handles complex numbers, and can read many different conventions.

The Python API is built on top of netCDF4-python, so only a very simple change to xarray is needed to use it:

```diff
modified   xarray/backends/api.py
@@ -115,7 +115,10 @@ def _get_default_engine_gz() -> Literal[""scipy""]:
 def _get_default_engine_netcdf() -> Literal[""netcdf4"", ""scipy""]:
     engine: Literal[""netcdf4"", ""scipy""]
     try:
-        import netCDF4  # noqa: F401
+        try:
+            import nc_complex  # noqa: F401
+        except ImportError:
+            import netCDF4  # noqa: F401
 
         engine = ""netcdf4""
     except ImportError:  # pragma: no cover
modified   xarray/backends/netCDF4_.py
@@ -327,7 +327,10 @@ class NetCDF4DataStore(WritableCFDataStore):
     def __init__(
         self, manager, group=None, mode=None, lock=NETCDF4_PYTHON_LOCK, autoclose=False
     ):
-        import netCDF4
+        try:
+            import nc_complex as netCDF4
+        except ImportError:
+            import netCDF4
 
         if isinstance(manager, netCDF4.Dataset):
             if group is None:
@@ -364,7 +367,10 @@ class NetCDF4DataStore(WritableCFDataStore):
         lock_maker=None,
         autoclose=False,
     ):
-        import netCDF4
+        try:
+            import nc_complex as netCDF4
+        except ImportError:
+            import netCDF4
 
         if isinstance(filename, os.PathLike):
             filename = os.fspath(filename)
```

and then it works out of the box:

```python
import numpy as np
import xarray as xr

complex_array = np.array([0 + 0j, 1 + 0j, 0 + 1j, 1 + 1j, 0.25 + 0.75j], dtype=""c16"")

ds = xr.Dataset({""complex_data"": (""x"", complex_array)})
ds.to_netcdf(""test.nc"")

with xr.open_dataset(""test.nc"") as df:
    print(df.complex_data)
    assert ds == df

# <xarray.DataArray 'complex_data' (x: 5)>
# [5 values with dtype=complex128]
# Dimensions without coordinates: x
```

If the library is built against the latest `main` of netCDF-C, then it also supports files written by `h5netcdf`. And while the package isn't on PyPI yet, [built wheels with this feature are available from CI jobs](https://github.com/PlasmaFAIR/nc-complex/actions/runs/6459506996).

`nc_complex` is not quite ready yet, but I wanted to gauge interest for adding it as an optional replacement for `netCDF4` in xarray.

### Describe alternatives you've considered

_No response_

### Additional context

_No response_","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/8288/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,completed,13221727,issue