felipecrv commented on code in PR #38394:
URL: https://github.com/apache/arrow/pull/38394#discussion_r1428388935
##########
cpp/src/arrow/compute/kernels/vector_hash.cc:
##########
@@ -457,14 +457,17 @@ class DictionaryHashKernel : public HashKernel {
// A better approach may be to run the kernel over each individual chunk,
// and then hash-aggregate all results (for example sum-group-by for
// the "value_counts" kernel).
+ if (dictionary_unifier_ == nullptr) {
+ ARROW_ASSIGN_OR_RAISE(dictionary_unifier_,
+ DictionaryUnifier::Make(dictionary_->type()));
+ RETURN_NOT_OK(dictionary_unifier_->Unify(*dictionary_));
+ }
auto out_dict_type = dictionary_->type();
std::shared_ptr<Buffer> transpose_map;
std::shared_ptr<Array> out_dict;
- ARROW_ASSIGN_OR_RAISE(auto unifier,
DictionaryUnifier::Make(out_dict_type));
- ARROW_CHECK_OK(unifier->Unify(*dictionary_));
- ARROW_CHECK_OK(unifier->Unify(*arr_dict, &transpose_map));
- ARROW_CHECK_OK(unifier->GetResult(&out_dict_type, &out_dict));
+ RETURN_NOT_OK(dictionary_unifier_->Unify(*arr_dict, &transpose_map));
+ RETURN_NOT_OK(dictionary_unifier_->GetResult(&out_dict_type, &out_dict));
dictionary_ = out_dict;
Review Comment:
Do we even need `dictionary_` to be a member variable now? Wouldn't it
suffice to perform a single `DictionaryUnifier::GetResult` call at the end?
##########
cpp/src/arrow/compute/kernels/vector_hash.cc:
##########
@@ -457,14 +457,17 @@ class DictionaryHashKernel : public HashKernel {
// A better approach may be to run the kernel over each individual chunk,
// and then hash-aggregate all results (for example sum-group-by for
// the "value_counts" kernel).
+ if (dictionary_unifier_ == nullptr) {
+ ARROW_ASSIGN_OR_RAISE(dictionary_unifier_,
+ DictionaryUnifier::Make(dictionary_->type()));
+ RETURN_NOT_OK(dictionary_unifier_->Unify(*dictionary_));
+ }
auto out_dict_type = dictionary_->type();
std::shared_ptr<Buffer> transpose_map;
std::shared_ptr<Array> out_dict;
- ARROW_ASSIGN_OR_RAISE(auto unifier,
DictionaryUnifier::Make(out_dict_type));
- ARROW_CHECK_OK(unifier->Unify(*dictionary_));
- ARROW_CHECK_OK(unifier->Unify(*arr_dict, &transpose_map));
- ARROW_CHECK_OK(unifier->GetResult(&out_dict_type, &out_dict));
+ RETURN_NOT_OK(dictionary_unifier_->Unify(*arr_dict, &transpose_map));
+ RETURN_NOT_OK(dictionary_unifier_->GetResult(&out_dict_type, &out_dict));
dictionary_ = out_dict;
Review Comment:
Documentation for `DictionaryUnifier::GetResult` says the unifier can't be
re-used after a call to `GetResult` [1].
My suggestion (that *I think* will work well):
Rename `dictionary_` to `first_dictionary_` and change `Append(arr)` to
transition through this state machine on each call:
```cpp
```cpp
//
--------------------------------------------------------------------------------------------------------------
// Current State Next State
//
--------------------------------------------------------------------------------------------------------------
// !first_dictionary_ && !dictionary_unifier_ --> first_dictionary_ =
arr_dict_
// UNCHANGED
dictionary_unifier_
//
--------------------------------------------------------------------------------------------------------------
// first_dictionary_ && !dictionary_unifier_ --> if
!first_dictionary_.Equals(arr_dict) then
// dictionary_unifier_
= unify(first_dictionary_, arr_dict)
// first_dictionary_ =
nullptr
// else
// UNCHANGED
first_dictionary_, dictionary_unifier_
// end
//
--------------------------------------------------------------------------------------------------------------
dictionary_unifier_ --> dictionary_unifier_ =
unify(dictionary_unifier_, arr_dict)
```
You will then have to re-think how `dictionary_value_type` and `dictionary`
work below.
[1]
https://github.com/apache/arrow/blob/main/cpp/src/arrow/array/array_dict.h#L169
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