[GitHub] [arrow-rs] alamb commented on a change in pull request #1469: Implement ArrayEqual for UnionArray

[GitBox <gi...@apache.org>]

alamb commented on a change in pull request #1469:
URL: https://github.com/apache/arrow-rs/pull/1469#discussion_r837807789



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File path: arrow/src/array/equal/union.rs
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@@ -0,0 +1,171 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use crate::datatypes::Field;
+use crate::{
+    array::ArrayData, buffer::Buffer, datatypes::DataType, datatypes::UnionMode,
+};
+
+use super::{
+    equal_range, equal_values, utils::child_logical_null_buffer, utils::equal_nulls,
+};
+
+// Checks if corresponding slots in two UnionArrays are same data types
+fn equal_types(
+    lhs_fields: &[Field],
+    rhs_fields: &[Field],
+    lhs_type_ids: &[i8],
+    rhs_type_ids: &[i8],
+) -> bool {
+    let lhs_slots_types = lhs_type_ids
+        .iter()
+        .map(|type_id| lhs_fields.get(*type_id as usize).unwrap().data_type());
+
+    let rhs_slots_types = rhs_type_ids
+        .iter()
+        .map(|type_id| rhs_fields.get(*type_id as usize).unwrap().data_type());
+
+    lhs_slots_types.zip(rhs_slots_types).all(|(l, r)| l == r)
+}
+
+fn equal_dense(
+    lhs: &ArrayData,
+    rhs: &ArrayData,
+    lhs_type_ids: &[i8],
+    rhs_type_ids: &[i8],
+    lhs_offsets: &[i32],
+    rhs_offsets: &[i32],
+) -> bool {
+    let offsets = lhs_offsets.iter().zip(rhs_offsets.iter());
+
+    lhs_type_ids
+        .iter()
+        .zip(rhs_type_ids.iter())
+        .zip(offsets)
+        .all(|((l_type_id, r_type_id), (l_offset, r_offset))| {
+            let lhs_values = &lhs.child_data()[*l_type_id as usize];
+            let rhs_values = &rhs.child_data()[*r_type_id as usize];
+
+            equal_values(
+                lhs_values,
+                rhs_values,
+                None,
+                None,
+                *l_offset as usize,
+                *r_offset as usize,
+                1,
+            )
+        })
+}
+
+#[allow(clippy::too_many_arguments)]
+fn equal_sparse(

Review comment:
       I suppose it really does come down to "what does it mean for two `UnionArray`s to be equal"?
   
   
   Can it ever be true that `UnionArray(Int, Utf8)` be equal to `UnionArray(Utf8, Int)`?
   
   Given my reading of the cpp `ArrayEquals` code in https://github.com/apache/arrow/blob/master/cpp/src/arrow/compare.cc it seems to me that two arrays are only ever "equal" if their datatypes are (exactly) equal. 
   
   Maybe we could follow the cpp implementation -- both for consistency as well as for simplicity?




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