Function EnsureHashDictionary

cpp/src/arrow/compute/kernels/vector_hash.cc:654–663

Return the dictionary from the hash kernel or allocate an empty one. Required because on empty inputs, we don't ever see the input and hence have no dictionary.

// Required because on empty inputs, we don't ever see the input and
// hence have no dictionary.
Result<std::shared_ptr<ArrayData>> EnsureHashDictionary(KernelContext* ctx,
                                                        DictionaryHashKernel* hash) {
  ARROW_ASSIGN_OR_RAISE(auto dict, hash->dictionary());
  if (dict) {
    return dict->data();
  }
  ARROW_ASSIGN_OR_RAISE(auto null, MakeArrayOfNull(hash->dictionary_value_type(),
                                                   /*length=*/0, ctx->memory_pool()));
  return null->data();
}

Status UniqueFinalizeDictionary(KernelContext* ctx, std::vector<Datum>* out) {
  RETURN_NOT_OK(UniqueFinalize(ctx, out));