adamreeve commented on code in PR #41144:
URL: https://github.com/apache/arrow/pull/41144#discussion_r1560404277
##########
csharp/src/Apache.Arrow/Arrays/ArrayData.cs:
##########
@@ -125,5 +155,69 @@ public ArrayData Clone(MemoryAllocator allocator = default)
Children?.Select(b => b.Clone(allocator))?.ToArray(),
Dictionary?.Clone(allocator));
}
+
+ private int ComputeNullCount()
+ {
+ if (DataType.TypeId == ArrowTypeId.Union)
+ {
+ return ((UnionType)DataType).Mode switch
+ {
+ UnionMode.Sparse => ComputeSparseUnionNullCount(),
+ UnionMode.Dense => ComputeDenseUnionNullCount(),
+ _ => throw new InvalidOperationException("unknown union
mode in null count computation")
+ };
+ }
+
+ if (Buffers == null || Buffers.Length == 0 || Buffers[0].IsEmpty)
+ {
+ return 0;
+ }
+
+ // Note: Dictionary arrays may be logically null if there is a
null in the dictionary values,
+ // but this isn't accounted for by the IArrowArray.IsNull
implementation,
+ // so we maintain consistency with that behaviour here.
Review Comment:
The C++ implementation actually has a separate `ComputeLogicalNullCount`
method on `ArrayData` and `Array` that handles union arrays, dictionary arrays
and run end encoded arrays, and there the `null_count` for union arrays always
returns 0. The C# `UnionArray.IsValid` method depends on the `NullCount` value
though, so I figured it made sense to compute the actual null count for union
arrays.
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