fix: Raise if merge non-global categoricals in unpivot (#19826)

pola-rs · Nov 17, 2024 · 245d549 · 245d549
1 parent 5210d99
commit 245d549
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diff --git a/crates/polars-core/src/utils/supertype.rs b/crates/polars-core/src/utils/supertype.rs
@@ -524,6 +524,7 @@ pub fn merge_dtypes_many<I: IntoIterator<Item = D> + Clone, D: AsRef<DataType>>(
             let DataType::Categorical(Some(rm), _) = first_dt else {
                 unreachable!()
             };
+            polars_ensure!(matches!(rm.as_ref(), RevMapping::Global(_, _, _)), ComputeError: "global string cache must be set to merge categorical columns");
 
             let mut merger = GlobalRevMapMerger::new(rm.clone());
 

diff --git a/py-polars/tests/unit/operations/test_unpivot.py b/py-polars/tests/unit/operations/test_unpivot.py
@@ -113,3 +113,8 @@ def test_unpivot_categorical_global() -> None:
         "variable": ["1", "1", "2", "2"],
         "value": ["a", "b", "b", "c"],
     }
+
+
+def test_unpivot_categorical_raise_19770() -> None:
+    with pytest.raises(pl.exceptions.ComputeError):
+        (pl.DataFrame({"x": ["foo"]}).cast(pl.Categorical).unpivot())