[GitHub] [arrow] js8544 commented on a diff in pull request #36906: GH-36905: [C++] Add support for SparseUnion to selection functions

["js8544 (via GitHub)" <gi...@apache.org>]

js8544 commented on code in PR #36906:
URL: https://github.com/apache/arrow/pull/36906#discussion_r1288798946


##########
cpp/src/arrow/compute/kernels/vector_selection_internal.cc:
##########
@@ -741,6 +741,63 @@ struct DenseUnionSelectionImpl
   }
 };
 
+struct SparseUnionSelectionImpl
+    : public Selection<SparseUnionSelectionImpl, SparseUnionType> {
+  using Base = Selection<SparseUnionSelectionImpl, SparseUnionType>;
+  LIFT_BASE_MEMBERS();
+
+  TypedBufferBuilder<int8_t> child_id_buffer_builder_;
+  std::vector<int8_t> type_codes_;
+
+  SparseUnionSelectionImpl(KernelContext* ctx, const ExecSpan& batch,
+                           int64_t output_length, ExecResult* out)
+      : Base(ctx, batch, output_length, out),
+        child_id_buffer_builder_(ctx->memory_pool()),
+        type_codes_(checked_cast<const UnionType&>(*this->values.type).type_codes()) {}
+
+  template <typename Adapter>
+  Status GenerateOutput() {
+    SparseUnionArray typed_values(this->values.ToArrayData());
+    Adapter adapter(this);
+    RETURN_NOT_OK(adapter.Generate(
+        [&](int64_t index) {
+          int8_t child_id = typed_values.child_id(index);
+          child_id_buffer_builder_.UnsafeAppend(type_codes_[child_id]);

Review Comment:
   Fixed



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