Add test

Author: dcherian

xarray/tests/indexes.py

@@ -1,4 +1,7 @@
+from collections.abc import Hashable, Iterable, Sequence
+
 from xarray.core.indexes import Index, PandasIndex
+from xarray.core.types import Self
 
 
 class ScalarIndex(Index):
@@ -26,11 +29,34 @@ def from_variables(cls, variables, *, options):
             y=PandasIndex.from_variables({"y": variables["y"]}, options=options),
         )
 
+    def create_variables(self, variables):
+        return self.x.create_variables() | self.y.create_variables()
+
     def equals(self, other, exclude=None):
         x_eq = True if self.x.dim in exclude else self.x.equals(other.x)
         y_eq = True if self.y.dim in exclude else self.y.equals(other.y)
         return x_eq and y_eq
 
+    @classmethod
+    def concat(
+        cls,
+        indexes: Sequence[Self],
+        dim: Hashable,
+        positions: Iterable[Iterable[int]] | None = None,
+    ) -> Self:
+        first = next(iter(indexes))
+        if dim == "x":
+            newx = PandasIndex.concat(
+                tuple(i.x for i in indexes), dim=dim, positions=positions
+            )
+            newy = first.y
+        elif dim == "y":
+            newx = first.x
+            newy = PandasIndex.concat(
+                tuple(i.y for i in indexes), dim=dim, positions=positions
+            )
+        return cls(x=newx, y=newy)
+
 
 class MultiCoordIndex(Index):
     def __init__(self, idx1, idx2):

xarray/tests/test_concat.py

@@ -8,7 +8,7 @@
 import pandas as pd
 import pytest
 
-from xarray import DataArray, Dataset, Variable, concat
+from xarray import AlignmentError, DataArray, Dataset, Variable, concat
 from xarray.core import dtypes
 from xarray.core.coordinates import Coordinates
 from xarray.core.indexes import PandasIndex
@@ -22,6 +22,7 @@
     assert_identical,
     requires_dask,
 )
+from xarray.tests.indexes import XYIndex
 from xarray.tests.test_dataset import create_test_data
 
 if TYPE_CHECKING:
@@ -1379,3 +1380,48 @@ def test_concat_index_not_same_dim() -> None:
         match=r"Cannot concatenate along dimension 'x' indexes with dimensions.*",
     ):
         concat([ds1, ds2], dim="x")
+
+
+def test_concat_multi_dim_index() -> None:
+    ds1 = (
+        Dataset(
+            {"foo": (("x", "y"), np.random.randn(2, 2))},
+            coords={"x": [1, 2], "y": [3, 4]},
+        )
+        .drop_indexes(["x", "y"])
+        .set_xindex(["x", "y"], XYIndex)
+    )
+    ds2 = (
+        Dataset(
+            {"foo": (("x", "y"), np.random.randn(2, 2))},
+            coords={"x": [1, 2], "y": [5, 6]},
+        )
+        .drop_indexes(["x", "y"])
+        .set_xindex(["x", "y"], XYIndex)
+    )
+
+    expected = (
+        Dataset(
+            {
+                "foo": (
+                    ("x", "y"),
+                    np.concatenate([ds1.foo.data, ds2.foo.data], axis=-1),
+                )
+            },
+            coords={"x": [1, 2], "y": [3, 4, 5, 6]},
+        )
+        .drop_indexes(["x", "y"])
+        .set_xindex(["x", "y"], XYIndex)
+    )
+    # note: missing 'override'
+    for join in ["inner", "outer", "exact", "left", "right"]:
+        actual = concat([ds1, ds2], dim="y", join=join)
+        assert_identical(actual, expected, check_default_indexes=False)
+
+    with pytest.raises(AlignmentError):
+        actual = concat([ds1, ds2], dim="x", join="exact")
+
+    # TODO: fix these, or raise better error message
+    with pytest.raises(AssertionError):
+        for join in ["left", "right"]:
+            actual = concat([ds1, ds2], dim="x", join=join)