grid.refine raises incomprehensible ValueError when there is a data variable with dtype object present in the dataset

[OnnoEbbens]

When I add the code below after the 4th code cell in the example notebook 03_local_grid_refinement I get the ValueError below. The origin of the error is a problem when using ds.interp to refine the data variables in the dataset. The interp function gives a different result when it has to modify data variables with type object.

I will try to fix this by removing the data variables with type object from the dataset. I think in most cases this won't be a problem. If it is we can try to think of a method to refine arrays of type object. This should be doable for the method 'nearest'.

import numpy as np
ones = np.ones((ds.dims['y'], ds.dims['x']),dtype=str)
ds['davar_str'] = (('y','x'), ones)
ds = nlmod.grid.refine(ds)

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
[~\AppData\Local\Temp\ipykernel_7768\2380354137.py](https://file+.vscode-resource.vscode-cdn.net/c%3A/Users/oebbe/02_python/nlmod/docs/examples/~/AppData/Local/Temp/ipykernel_7768/2380354137.py) in ()
      2 ones = np.ones((ds.dims['y'], ds.dims['x']),dtype=str)
      3 ds['davar_str'] = (('y','x'), ones)
----> 4 ds = nlmod.grid.refine(ds)

[~\02_python\nlmod\nlmod\dims\grid.py](https://file+.vscode-resource.vscode-cdn.net/c%3A/Users/oebbe/02_python/nlmod/docs/examples/~/02_python/nlmod/nlmod/dims/grid.py) in refine(ds, model_ws, refinement_features, exe_name, remove_nan_layers, model_coordinates)
    423     gridprops = g.get_gridprops_disv()
    424     gridprops["area"] = g.get_area()
--> 425     ds = ds_to_gridprops(ds, gridprops=gridprops)
    426     # recalculate idomain, as the interpolation changes idomain to floats
    427     ds = set_idomain(ds, remove_nan_layers=remove_nan_layers)

[~\02_python\nlmod\nlmod\dims\grid.py](https://file+.vscode-resource.vscode-cdn.net/c%3A/Users/oebbe/02_python/nlmod/docs/examples/~/02_python/nlmod/nlmod/dims/grid.py) in ds_to_gridprops(ds_in, gridprops, method, nodata)
    475         # only keep the first layer of area
    476         area = gridprops["area"][: len(ds_out["icell2d"])]
--> 477         ds_out["area"] = ("icell2d", area)
    478 
    479     # add information about the vertices

[c:\Users\oebbe\anaconda3\envs\nlmod\lib\site-packages\xarray\core\dataset.py](file:///C:/Users/oebbe/anaconda3/envs/nlmod/lib/site-packages/xarray/core/dataset.py) in __setitem__(self, key, value)
   1495                     "object can be stored under a single key."
   1496                 )
-> 1497             self.update({key: value})
   1498 
   1499         elif utils.iterable_of_hashable(key):

[c:\Users\oebbe\anaconda3\envs\nlmod\lib\site-packages\xarray\core\dataset.py](file:///C:/Users/oebbe/anaconda3/envs/nlmod/lib/site-packages/xarray/core/dataset.py) in update(self, other)
   4951         Dataset.merge
   4952         """
-> 4953         merge_result = dataset_update_method(self, other)
   4954         return self._replace(inplace=True, **merge_result._asdict())
   4955 

[c:\Users\oebbe\anaconda3\envs\nlmod\lib\site-packages\xarray\core\merge.py](file:///C:/Users/oebbe/anaconda3/envs/nlmod/lib/site-packages/xarray/core/merge.py) in dataset_update_method(dataset, other)
   1091                     other[key] = value.drop_vars(coord_names)
   1092 
-> 1093     return merge_core(
   1094         [dataset, other],
   1095         priority_arg=1,

[c:\Users\oebbe\anaconda3\envs\nlmod\lib\site-packages\xarray\core\merge.py](file:///C:/Users/oebbe/anaconda3/envs/nlmod/lib/site-packages/xarray/core/merge.py) in merge_core(objects, compat, join, combine_attrs, priority_arg, explicit_coords, indexes, fill_value)
    739 
    740     coerced = coerce_pandas_values(objects)
--> 741     aligned = deep_align(
    742         coerced, join=join, copy=False, indexes=indexes, fill_value=fill_value
    743     )

[c:\Users\oebbe\anaconda3\envs\nlmod\lib\site-packages\xarray\core\alignment.py](file:///C:/Users/oebbe/anaconda3/envs/nlmod/lib/site-packages/xarray/core/alignment.py) in deep_align(objects, join, copy, indexes, exclude, raise_on_invalid, fill_value)
    848             out.append(variables)
    849 
--> 850     aligned = align(
    851         *targets,
    852         join=join,

[c:\Users\oebbe\anaconda3\envs\nlmod\lib\site-packages\xarray\core\alignment.py](file:///C:/Users/oebbe/anaconda3/envs/nlmod/lib/site-packages/xarray/core/alignment.py) in align(join, copy, indexes, exclude, fill_value, *objects)
    785         fill_value=fill_value,
    786     )
--> 787     aligner.align()
    788     return aligner.results
    789 

[c:\Users\oebbe\anaconda3\envs\nlmod\lib\site-packages\xarray\core\alignment.py](file:///C:/Users/oebbe/anaconda3/envs/nlmod/lib/site-packages/xarray/core/alignment.py) in align(self)
    569         self.find_matching_indexes()
    570         self.find_matching_unindexed_dims()
--> 571         self.assert_no_index_conflict()
    572         self.align_indexes()
    573         self.assert_unindexed_dim_sizes_equal()

[c:\Users\oebbe\anaconda3\envs\nlmod\lib\site-packages\xarray\core\alignment.py](file:///C:/Users/oebbe/anaconda3/envs/nlmod/lib/site-packages/xarray/core/alignment.py) in assert_no_index_conflict(self)
    312                     f"{k!r} ({v} conflicting indexes)" for k, v in dup.items()
    313                 )
--> 314                 raise ValueError(
    315                     "cannot re-index or align objects with conflicting indexes found for "
    316                     f"the following {msg}: {items_msg}\n"

ValueError: cannot re-index or align objects with conflicting indexes found for the following dimensions: 'icell2d' (2 conflicting indexes)
Conflicting indexes may occur when
- they relate to different sets of coordinate and/or dimension names
- they don't have the same type
- they may be used to reindex data along common dimensions