Fix for Graph.describe() when the graph has a string index (#759) (#760)

* numba mode fix when graph has string index

* typing

* Apply suggestions from code review

Co-authored-by: Martin Fleischmann <[email protected]>

---------

Co-authored-by: Martin Fleischmann <[email protected]>

Author: u3ks

libpysal/graph/base.py

@@ -2651,6 +2651,10 @@ def describe(
         if (y.index != self.unique_ids).all():
             raise ValueError("The values index is not aligned with the graph index.")
 
+        # reset numerical index to enable numba functionality
+        if not isinstance(y.index.dtype, int | float):
+            y = y.reset_index(drop=True)
+
         if q is None:
             grouper = y.take(self._adjacency.index.codes[1]).groupby(
                 self._adjacency.index.codes[0], sort=False

libpysal/graph/tests/test_base.py

@@ -1327,7 +1327,7 @@ def test_describe(self):
         # test with isolates and string index
         nybb_contig = graph.Graph.build_contiguity(self.nybb, rook=False)
         stats = nybb_contig.describe(
-            self.nybb.geometry.area, statistics=["count", "sum"]
+            self.nybb.geometry.area, statistics=["count", "sum", "mode"]
         )
         ## all isolate values should be nan
         assert stats.loc["Staten Island"].isna().all()
@@ -1348,6 +1348,13 @@ def test_describe(self):
             check_names=False,
         )
 
+        y = self.nybb.geometry.area
+        for i in nybb_contig.unique_ids:
+            neigh_vals = y.loc[nybb_contig[i].index.values]
+            expected = neigh_vals.mode().iloc[0] if neigh_vals.shape[0] else 0
+            res = stats.loc[i]["mode"]
+            assert res == expected
+
         ## test passing ndarray
         stats1 = nybb_contig.describe(self.nybb.geometry.area, statistics=["sum"])[
             "sum"