Xarray: .sel method gives error with float32 values

[hdsingh]

.sel method gives error when it is used to select float32 values however it works fine for float64
Example:

import xarray as xr
import numpy as np

a = np.asarray([0.    , 0.111, 0.222, 0.333], dtype='float32')
ds = xr.Dataset(coords={'a': (['a'],a )})
ds.a.sel({'a': 0.111})

Error Traceback:

KeyError                                  Traceback (most recent call last)
~/anaconda3/envs/check3/lib/python3.7/site-packages/pandas/core/indexes/base.py in get_loc(self, key, method, tolerance)
   2656             try:
-> 2657                 return self._engine.get_loc(key)
   2658             except KeyError:

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.Float64HashTable.get_item()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.Float64HashTable.get_item()

KeyError: 0.111

During handling of the above exception, another exception occurred:

KeyError                                  Traceback (most recent call last)
<ipython-input-7-b4190c1d9580> in <module>
      4 a = np.asarray([0.    , 0.111, 0.222, 0.333], dtype='float32')
      5 ds = xr.Dataset(coords={'a': (['a'],a )})
----> 6 ds.a.sel({'a': 0.111})
      7 ds.a.sel({'a': 0.111}, method= 'nearest')

~/anaconda3/envs/check3/lib/python3.7/site-packages/xarray/core/dataarray.py in sel(self, indexers, method, tolerance, drop, **indexers_kwargs)
    853         ds = self._to_temp_dataset().sel(
    854             indexers=indexers, drop=drop, method=method, tolerance=tolerance,
--> 855             **indexers_kwargs)
    856         return self._from_temp_dataset(ds)
    857 

~/anaconda3/envs/check3/lib/python3.7/site-packages/xarray/core/dataset.py in sel(self, indexers, method, tolerance, drop, **indexers_kwargs)
   1729         indexers = either_dict_or_kwargs(indexers, indexers_kwargs, 'sel')
   1730         pos_indexers, new_indexes = remap_label_indexers(
-> 1731             self, indexers=indexers, method=method, tolerance=tolerance)
   1732         result = self.isel(indexers=pos_indexers, drop=drop)
   1733         return result._overwrite_indexes(new_indexes)

~/anaconda3/envs/check3/lib/python3.7/site-packages/xarray/core/coordinates.py in remap_label_indexers(obj, indexers, method, tolerance, **indexers_kwargs)
    315 
    316     pos_indexers, new_indexes = indexing.remap_label_indexers(
--> 317         obj, v_indexers, method=method, tolerance=tolerance
    318     )
    319     # attach indexer's coordinate to pos_indexers

~/anaconda3/envs/check3/lib/python3.7/site-packages/xarray/core/indexing.py in remap_label_indexers(data_obj, indexers, method, tolerance)
    250         else:
    251             idxr, new_idx = convert_label_indexer(index, label,
--> 252                                                   dim, method, tolerance)
    253             pos_indexers[dim] = idxr
    254             if new_idx is not None:

~/anaconda3/envs/check3/lib/python3.7/site-packages/xarray/core/indexing.py in convert_label_indexer(index, label, index_name, method, tolerance)
    179                 indexer, new_index = index.get_loc_level(label.item(), level=0)
    180             else:
--> 181                 indexer = get_loc(index, label.item(), method, tolerance)
    182         elif label.dtype.kind == 'b':
    183             indexer = label

~/anaconda3/envs/check3/lib/python3.7/site-packages/xarray/core/indexing.py in get_loc(index, label, method, tolerance)
    106 def get_loc(index, label, method=None, tolerance=None):
    107     kwargs = _index_method_kwargs(method, tolerance)
--> 108     return index.get_loc(label, **kwargs)
    109 
    110 

~/anaconda3/envs/check3/lib/python3.7/site-packages/pandas/core/indexes/numeric.py in get_loc(self, key, method, tolerance)
    434             pass
    435         return super(Float64Index, self).get_loc(key, method=method,
--> 436                                                  tolerance=tolerance)
    437 
    438     @cache_readonly

~/anaconda3/envs/check3/lib/python3.7/site-packages/pandas/core/indexes/base.py in get_loc(self, key, method, tolerance)
   2657                 return self._engine.get_loc(key)
   2658             except KeyError:
-> 2659                 return self._engine.get_loc(self._maybe_cast_indexer(key))
   2660         indexer = self.get_indexer([key], method=method, tolerance=tolerance)
   2661         if indexer.ndim > 1 or indexer.size > 1:

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.Float64HashTable.get_item()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.Float64HashTable.get_item()

KeyError: 0.111

xarray version: 0.12.1
numpy version: 1.16.3

[dcherian]

da.sel(a=np.float32(0.111)) works so maybe we should cast to the dtype of the coordinate?

[shoyer]

da.sel(a=np.float32(0.111)) works so maybe we should cast to the dtype of the coordinate?

Sounds like a good idea to me!

[dcherian]

@hdsingh Any interest in sending in a PR?

[hdsingh]

As of now I am a bit short on time due to GSOC project. I may not be able to look into this for next 2-3 weeks.

[HasanAhmadQ7]

@dcherian I would like to send a PR and work on this issue if there is no problem in this.

[dcherian]

@HasanAhmadQ7 go for it!

[HasanAhmadQ7]

@dcherian I sent a PR last week. Any feedback would be appreciated

[HasanAhmadQ7]

The case also arises if coords are float16. e.g.

        data_values = np.arange(4)
        coord_values_16 = np.asarray(float_values, dtype='float16')
        array_16 = DataArray(data_values, [('float16_coord', coord_values_16)])
        array_16.sel(float16_coord=float_values[1:3])