fix[rust]: maintain logical type in value counts (#4460)

polars/polars-ops/src/series/ops/various.rs

@@ -8,8 +8,7 @@ pub trait SeriesMethods: SeriesSealed {
     /// Create a [`DataFrame`] with the unique `values` of this [`Series`] and a column `"counts"`
     /// with dtype [`IdxType`]
     fn value_counts(&self, multithreaded: bool, sorted: bool) -> Result<DataFrame> {
-        let s = self.as_series().to_physical_repr();
-        let s = s.as_ref();
+        let s = self.as_series();
         // we need to sort here as well in case of `maintain_order` because duplicates behavior is undefined
         let groups = s.group_tuples(multithreaded, sorted);
         let values = unsafe { s.agg_first(&groups) };

py-polars/tests/test_struct.py

@@ -136,6 +136,16 @@ def test_value_counts_expr() -> None:
     ]
 
 
+def test_value_counts_logical_type() -> None:
+    # test logical type
+    df = pl.DataFrame({"a": ["b", "c"]}).with_column(
+        pl.col("a").cast(pl.Categorical).alias("ac")
+    )
+    out = df.select([pl.all().value_counts()])
+    assert out["ac"].struct.field("ac").dtype == pl.Categorical
+    assert out["a"].struct.field("a").dtype == pl.Utf8
+
+
 def test_nested_struct() -> None:
     df = pl.DataFrame({"d": [1, 2, 3], "e": ["foo", "bar", "biz"]})
     # Nest the datafame