fix(rust, python): include slice in sort fast path (#5247)

polars/polars-core/src/frame/mod.rs

@@ -1786,7 +1786,12 @@ impl DataFrame {
                 // no need to compute the sort indices and then take by these indices
                 // simply sort and return as frame
                 if self.width() == 1 && self.check_name_to_idx(s.name()).is_ok() {
-                    return Ok(s.sort_with(options).into_frame());
+                    let mut out = s.sort_with(options);
+                    if let Some((offset, len)) = slice {
+                        out = out.slice(offset, len);
+                    }
+
+                    return Ok(out.into_frame());
                 }
                 s.argsort(options)
             }

py-polars/tests/unit/test_sort.py

@@ -265,3 +265,16 @@ def test_unset_sorted_flag_after_extend() -> None:
     df = df1.groupby("Add").agg([pl.col("Batch").min()]).sort("Add")
     assert df["Add"].flags["SORTED_ASC"]
     assert df.to_dict(False) == {"Add": [37, 41], "Batch": [48, 49]}
+
+
+def test_sort_slice_fast_path_5245() -> None:
+    df = pl.DataFrame(
+        {
+            "foo": ["f", "c", "b", "a"],
+            "bar": [1, 2, 3, 4],
+        }
+    ).lazy()
+
+    assert df.sort("foo").limit(1).select("foo").collect().to_dict(False) == {
+        "foo": ["a"]
+    }