logic update

Author: DHRUVA KUMAR KAUSHAL

doc/whats-new.rst

@@ -25,6 +25,12 @@ Deprecations
 Bug fixes
 ~~~~~~~~~
 
+- :py:meth:`Dataset.set_xindex` now raises a helpful error when a custom index
+  creates extra variables that don't match the provided coordinate names, instead
+  of silently ignoring them. The error message suggests using the factory method
+  pattern with :py:meth:`xarray.Coordinates.from_xindex` and
+  :py:meth:`Dataset.assign_coords` for advanced use cases (:issue:`10499`).
+  By `Dhruva Kumar Kaushal <https://github.com/dhruvak001>`_.
 
 Documentation
 ~~~~~~~~~~~~~

xarray/core/dataset.py

@@ -4940,6 +4940,20 @@ def set_xindex(
         if isinstance(index, PandasMultiIndex):
             coord_names = [index.dim] + list(coord_names)
 
+        # Check for extra variables that don't match the coordinate names
+        extra_vars = set(new_coord_vars) - set(coord_names)
+        if extra_vars:
+            extra_vars_str = ", ".join(f"'{name}'" for name in extra_vars)
+            coord_names_str = ", ".join(f"'{name}'" for name in coord_names)
+            raise ValueError(
+                f"The index created extra variables {extra_vars_str} that are not "
+                f"in the list of coordinates {coord_names_str}. "
+                f"Use a factory method pattern instead:\n"
+                f"  index = {index_cls.__name__}.from_variables(ds, {list(coord_names)!r})\n"
+                f"  coords = xr.Coordinates.from_xindex(index)\n"
+                f"  ds = ds.assign_coords(coords)"
+            )
+
         variables: dict[Hashable, Variable]
         indexes: dict[Hashable, Index]