BUG fix +test .sel method gives error with float32 values

doc/whats-new.rst

@@ -62,6 +62,9 @@ Bug fixes
 - XFAIL several tests which are expected to fail on ARM systems
   due to a ``datetime`` issue in NumPy (:issue:`2334`).
   By `Graham Inggs <https://github.com/ginggs>`_.
+- Fix KeyError that arises when using .sel method with float values
+  different from coords float type (:issue:`3137`).
+  By `Hasan Ahmad <https://github.com/HasanAhmadQ7>`_.
 - Fixed bug in ``combine_by_coords()`` causing a `ValueError` if the input had
   an unused dimension with coordinates which were not monotonic (:issue:`3150`).
   By `Tom Nicholas <http://github.com/TomNicholas>`_.

xarray/core/indexing.py

@@ -11,7 +11,7 @@
 from . import duck_array_ops, nputils, utils
 from .npcompat import DTypeLike
 from .pycompat import dask_array_type, integer_types
-from .utils import is_dict_like
+from .utils import is_dict_like, maybe_cast_to_coords_dtype
 
 
 def expanded_indexer(key, ndim):
@@ -269,6 +269,8 @@ def remap_label_indexers(data_obj, indexers, method=None, tolerance=None):
                 )
             pos_indexers[dim] = label
         else:
+            coords_dtype = data_obj.coords[dim].dtype
+            label = maybe_cast_to_coords_dtype(label, coords_dtype)
             idxr, new_idx = convert_label_indexer(index, label, dim, method, tolerance)
             pos_indexers[dim] = idxr
             if new_idx is not None:

xarray/core/utils.py

@@ -85,6 +85,12 @@ def _maybe_cast_to_cftimeindex(index: pd.Index) -> pd.Index:
         return index
 
 
+def maybe_cast_to_coords_dtype(label, coords_dtype):
+    if coords_dtype.kind == "f" and not isinstance(label, slice):
+        label = np.asarray(label, dtype=coords_dtype)
+    return label
+
+
 def safe_cast_to_index(array: Any) -> pd.Index:
     """Given an array, safely cast it to a pandas.Index.
 

xarray/tests/test_dataarray.py

@@ -928,6 +928,33 @@ def test_sel_dataarray_datetime(self):
         result = array.sel(delta=slice(array.delta[0], array.delta[-1]))
         assert_equal(result, array)
 
+    def test_sel_float(self):
+        data_values = np.arange(4)
+
+        # case coords are float32 and label is list of floats
+        float_values = [0.0, 0.111, 0.222, 0.333]
+        coord_values = np.asarray(float_values, dtype="float32")
+        array = DataArray(data_values, [("float32_coord", coord_values)])
+        expected = DataArray(data_values[1:3], [("float32_coord", coord_values[1:3])])
+        actual = array.sel(float32_coord=float_values[1:3])
+        # case coords are float16 and label is list of floats
+        coord_values_16 = np.asarray(float_values, dtype="float16")
+        expected_16 = DataArray(
+            data_values[1:3], [("float16_coord", coord_values_16[1:3])]
+        )
+        array_16 = DataArray(data_values, [("float16_coord", coord_values_16)])
+        actual_16 = array_16.sel(float16_coord=float_values[1:3])
+
+        # case coord, label are scalars
+        expected_scalar = DataArray(
+            data_values[2], coords={"float32_coord": coord_values[2]}
+        )
+        actual_scalar = array.sel(float32_coord=float_values[2])
+
+        assert_equal(expected, actual)
+        assert_equal(expected_scalar, actual_scalar)
+        assert_equal(expected_16, actual_16)
+
     def test_sel_no_index(self):
         array = DataArray(np.arange(10), dims="x")
         assert_identical(array[0], array.sel(x=0))