[GitHub] [arrow] jhorstmann commented on a change in pull request #8590: ARROW-10042: [Rust] BufferData's equality should depend on its capacity; ArrayData's equality should not depend on its BufferDatas' capacities' equality

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

jhorstmann commented on a change in pull request #8590:
URL: https://github.com/apache/arrow/pull/8590#discussion_r519011669



##########
File path: rust/arrow/src/array/data.rs
##########
@@ -211,57 +211,66 @@ impl ArrayData {
 
 impl PartialEq for ArrayData {
     fn eq(&self, other: &Self) -> bool {
-        assert_eq!(
-            self.data_type(),
-            other.data_type(),
-            "Data types not the same"
-        );
-        assert_eq!(self.len(), other.len(), "Lengths not the same");
-        // TODO: when adding tests for this, test that we can compare with arrays that have offsets
-        assert_eq!(self.offset(), other.offset(), "Offsets not the same");
-        assert_eq!(self.null_count(), other.null_count());
-        // compare buffers excluding padding
-        let self_buffers = self.buffers();
-        let other_buffers = other.buffers();
-        assert_eq!(self_buffers.len(), other_buffers.len());
-        self_buffers.iter().zip(other_buffers).for_each(|(s, o)| {
-            compare_buffer_regions(
-                s,
-                self.offset(), // TODO mul by data length
-                o,
-                other.offset(), // TODO mul by data len
-            );
-        });
-        // assert_eq!(self.buffers(), other.buffers());
-
-        assert_eq!(self.child_data(), other.child_data());
-        // null arrays can skip the null bitmap, thus only compare if there are no nulls
-        if self.null_count() != 0 || other.null_count() != 0 {
-            compare_buffer_regions(
+        self.data_type() == other.data_type()
+            && self.len() == other.len()
+            // TODO: when adding tests for this, test that we can compare with arrays that have
+            // offsets
+            && self.offset() == other.offset()

Review comment:
       I think the offset does not have to be equal. Consider a buffer `[1,2,3,4,1,2,3,4]` and two arrays referencing this buffer, one with offset 0 and len 4, the other with offset 4 and len 4. Both arrays should be considered to contain the same 4 elements. This also means the `compare_buffers` function needs to take the array length as additional parameter.




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