working with test

crates/polars-plan/src/dsl/function_expr/array.rs

@@ -57,7 +57,7 @@ impl ArrayFunction {
             #[cfg(feature = "array_count")]
             CountMatches => mapper.with_dtype(IDX_DTYPE),
             Shift => mapper.with_same_dtype(),
-            Explode => mapper.map_to_list_and_array_inner_dtype(),
+            Explode => mapper.try_map_to_array_inner_dtype(),
         }
     }
 }

crates/polars-plan/src/dsl/function_expr/schema.rs

@@ -486,6 +486,16 @@ impl<'a> FieldsMapper<'a> {
         Ok(first)
     }
 
+    #[cfg(feature = "dtype-array")]
+    /// Map the dtype to the dtype of the array elements, with typo validation.
+    pub fn try_map_to_array_inner_dtype(&self) -> PolarsResult<Field> {
+        let dt = self.fields[0].dtype();
+        match dt {
+            DataType::Array(_, _) => self.map_to_list_and_array_inner_dtype(),
+            _ => polars_bail!(InvalidOperation: "expected Array type, got: {}", dt),
+        }
+    }
+
     /// Map the dtypes to the "supertype" of a list of lists.
     pub fn map_to_list_supertype(&self) -> PolarsResult<Field> {
         self.try_map_dtypes(|dts| {

crates/polars-plan/src/plans/optimizer/simplify_expr/simplify_functions.rs

@@ -7,10 +7,11 @@ pub(super) fn optimize_functions(
     expr_arena: &mut Arena<AExpr>,
 ) -> PolarsResult<Option<AExpr>> {
     let out = match function {
-        // arr.explode() -> explode
+        #[cfg(feature = "dtype-array")]
+        // arr.explode() -> explode()
         FunctionExpr::ArrayExpr(ArrayFunction::Explode) => {
-            let input_input = input[0].node();
-            Some(AExpr::Explode(input_input))
+            let input_node = input[0].node();
+            Some(AExpr::Explode(input_node))
         },
         // is_null().any() -> null_count() > 0
         // is_not_null().any() ->  null_count() < len()

py-polars/tests/unit/operations/namespaces/array/test_array.py

@@ -6,7 +6,7 @@
 import pytest
 
 import polars as pl
-from polars.exceptions import ComputeError
+from polars.exceptions import ComputeError, InvalidOperationError
 from polars.testing import assert_frame_equal, assert_series_equal
 
 
@@ -449,3 +449,14 @@ def test_array_n_unique() -> None:
         {"n_unique": [2, 1, 1, None]}, schema={"n_unique": pl.UInt32}
     )
     assert_frame_equal(out, expected)
+
+
+def test_explode_19049() -> None:
+    df = pl.DataFrame({"a": [[1, 2, 3]]}, schema={"a": pl.Array(pl.Int64, 3)})
+    result_df = df.select(pl.col.a.arr.explode())
+    expected_df = pl.DataFrame({"a": [1, 2, 3]}, schema={"a": pl.Int64})
+    assert_frame_equal(result_df, expected_df)
+
+    df = pl.DataFrame({"a": [1, 2, 3]}, schema={"a": pl.Int64})
+    with pytest.raises(InvalidOperationError, match="expected Array type, got: i64"):
+        df.select(pl.col.a.arr.explode())