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GH-41198: [C#] Fix concatenation of union arrays #41226

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Apr 16, 2024
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GH-41198: [C#] Fix concatenation of union arrays #41226

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b4bf1cd
Fix concatenation of union arrays
adamreeve Apr 15, 2024
e8a4b0a
Check for overflow when adding to base offsets
adamreeve Apr 15, 2024
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22 changes: 15 additions & 7 deletions csharp/src/Apache.Arrow/Arrays/ArrayDataConcatenator.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -367,7 +367,7 @@ private ArrowBuffer ConcatenateUnionTypeBuffer()

foreach (ArrayData arrayData in _arrayDataList)
{
builder.Append(arrayData.Buffers[0]);
builder.Append(arrayData.Buffers[0].Span.Slice(arrayData.Offset, arrayData.Length));
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I'm using the offset here but I haven't tested this works fully with sliced arrays, I'll follow up on this in #41164.

}

return builder.Build(_allocator);
Expand All @@ -376,18 +376,26 @@ private ArrowBuffer ConcatenateUnionTypeBuffer()
private ArrowBuffer ConcatenateUnionOffsetBuffer()
{
var builder = new ArrowBuffer.Builder<int>(_totalLength);
int baseOffset = 0;
var typeCount = _arrayDataList.Count > 0 ? _arrayDataList[0].Children.Length : 0;
var baseOffsets = new int[typeCount];

foreach (ArrayData arrayData in _arrayDataList)
{
ReadOnlySpan<int> span = arrayData.Buffers[1].Span.CastTo<int>();
foreach (int offset in span)
ReadOnlySpan<byte> typeSpan = arrayData.Buffers[0].Span.Slice(arrayData.Offset, arrayData.Length);
ReadOnlySpan<int> offsetSpan = arrayData.Buffers[1].Span.CastTo<int>().Slice(arrayData.Offset, arrayData.Length);
for (int i = 0; i < arrayData.Length; ++i)
{
builder.Append(baseOffset + offset);
var typeId = typeSpan[i];
builder.Append(checked(baseOffsets[typeId] + offsetSpan[i]));
}

// The next offset must start from the current last offset.
baseOffset += span[arrayData.Length];
for (int i = 0; i < typeCount; ++i)
{
checked
{
baseOffsets[i] += arrayData.Children[i].Length;
}
}
}

return builder.Build(_allocator);
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9 changes: 2 additions & 7 deletions csharp/test/Apache.Arrow.Tests/ArrowArrayConcatenatorTests.cs
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Expand Up @@ -29,12 +29,6 @@ public void TestStandardCases()
{
foreach ((List<IArrowArray> testTargetArrayList, IArrowArray expectedArray) in GenerateTestData())
{
if (expectedArray is UnionArray)
{
// Union array concatenation is incorrect. See https://github.com/apache/arrow/issues/41198
continue;
}

IArrowArray actualArray = ArrowArrayConcatenator.Concatenate(testTargetArrayList);
ArrowReaderVerifier.CompareArrays(expectedArray, actualArray);
}
Expand Down Expand Up @@ -604,10 +598,11 @@ public void Visit(UnionType type)

for (int j = 0; j < dataList.Count; j++)
{
byte index = (byte)Math.Max(j % 3, 1);
byte index = (byte)Math.Min(j % 3, 1);
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I'm pretty sure this was the intended behaviour, otherwise the index == 0 branch below is never used.

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With the original code, the indexes would be 1, 1, 2, 1, 1, 2, etc.. With this change, the indexes would be 0, 1, 1, 0, 1, 1, etc.

int? intValue = (index == 1) ? dataList[j] : null;
string stringValue = (index == 1) ? null : dataList[j]?.ToString();
typeBuilder.Append(index);
typeResultBuilder.Append(index);

if (isDense)
{
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