c

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

@@ -1091,7 +1091,20 @@ impl Column {
         match self {
             Column::Series(s) => s.rechunk().into(),
             Column::Partitioned(_) => self.clone(),
-            Column::Scalar(_) => self.clone(),
+            Column::Scalar(s) => {
+                if s.lazy_as_materialized_series()
+                    .filter(|x| x.n_chunks() > 1)
+                    .is_some()
+                {
+                    Column::Scalar(ScalarColumn::new(
+                        s.name().clone(),
+                        s.scalar().clone(),
+                        s.len(),
+                    ))
+                } else {
+                    self.clone()
+                }
+            },
         }
     }
 
@@ -1700,7 +1713,8 @@ impl Column {
     pub fn n_chunks(&self) -> usize {
         match self {
             Column::Series(s) => s.n_chunks(),
-            Column::Scalar(_) | Column::Partitioned(_) => 1,
+            Column::Scalar(s) => s.lazy_as_materialized_series().map_or(1, |x| x.n_chunks()),
+            Column::Partitioned(_) => 1,
         }
     }
 

py-polars/tests/unit/interop/test_interop.py

@@ -857,3 +857,8 @@ def test_from_arrow_string_cache_20271() -> None:
         assert_series_equal(
             df.to_series().to_physical(), pl.Series("b", [3, 4]), check_dtypes=False
         )
+
+
+def test_to_arrow_empty_chunks_20627() -> None:
+    df = pl.concat(2 * [pl.Series([1])]).filter(pl.Series([False, True])).to_frame()
+    assert df.to_arrow().shape == (1, 1)

py-polars/tests/unit/test_scalar.py

@@ -79,3 +79,8 @@ def test_scalar_identification_function_expr_in_binary() -> None:
         pl.select(x).with_columns(o=pl.col("x").null_count() > 0),
         pl.select(x, o=False),
     )
+
+
+def test_scalar_rechunk_20627() -> None:
+    df = pl.concat(2 * [pl.Series([1])]).filter(pl.Series([False, True])).to_frame()
+    assert df.rechunk().to_series().n_chunks() == 1