Ensure dtype of reindex result matches dtype of the original DataArray (#7917)

* Ensure dtype of reindex result matches dtype of the original DataArray

* update what's new

Author: andersy005

doc/whats-new.rst

@@ -46,6 +46,8 @@ Bug fixes
   By `Mattia Almansi <https://github.com/malmans2>`_.
 - Don't call ``CachingFileManager.__del__`` on interpreter shutdown (:issue:`7814`, :pull:`7880`).
   By `Justus Magin <https://github.com/keewis>`_.
+- Ensure dtype of reindex result matches dtype of the original DataArray (:issue:`7299`, :pull:`7917`)
+  By `Anderson Banihirwe <https://github.com/andersy005>`_.
 
 Documentation
 ~~~~~~~~~~~~~

xarray/core/dtypes.py

@@ -74,7 +74,10 @@ def maybe_promote(dtype):
     else:
         dtype = object
         fill_value = np.nan
-    return np.dtype(dtype), fill_value
+
+    dtype = np.dtype(dtype)
+    fill_value = dtype.type(fill_value)
+    return dtype, fill_value
 
 
 NAT_TYPES = {np.datetime64("NaT").dtype, np.timedelta64("NaT").dtype}

xarray/tests/test_dataarray.py

@@ -1698,6 +1698,19 @@ def test_reindex_str_dtype(self, dtype) -> None:
         assert_identical(expected, actual)
         assert actual.dtype == expected.dtype
 
+    def test_reindex_empty_array_dtype(self) -> None:
+        # Dtype of reindex result should match dtype of the original DataArray.
+        # See GH issue #7299
+        x = xr.DataArray([], dims=("x",), coords={"x": []}).astype("float32")
+        y = x.reindex(x=[1.0, 2.0])
+
+        assert (
+            x.dtype == y.dtype
+        ), "Dtype of reindexed DataArray should match dtype of the original DataArray"
+        assert (
+            y.dtype == np.float32
+        ), "Dtype of reindexed DataArray should remain float32"
+
     def test_rename(self) -> None:
         da = xr.DataArray(
             [1, 2, 3], dims="dim", name="name", coords={"coord": ("dim", [5, 6, 7])}