[GitHub] [arrow] lidavidm commented on a change in pull request #10721: ARROW-11673 - [C++] Casting dictionary type to use different index type

[GitBox <gi...@apache.org>]

lidavidm commented on a change in pull request #10721:
URL: https://github.com/apache/arrow/pull/10721#discussion_r670384702



##########
File path: cpp/src/arrow/compute/kernels/scalar_cast_test.cc
##########
@@ -1911,5 +1911,35 @@ TEST(Cast, ExtensionTypeToIntDowncast) {
   }
 }
 
+TEST(Cast, DictTypeToAnotherDict) {
+  auto check_cast = [&](const std::shared_ptr<DataType>& in_type,
+                        const std::shared_ptr<DataType>& out_type,
+                        const std::string& json_str,
+                        const CastOptions& options = CastOptions()) {
+    auto arr = ArrayFromJSON(in_type, json_str);
+    auto exp = in_type->Equals(out_type) ? arr : ArrayFromJSON(out_type, json_str);
+    // this checks for scalars as well
+    CheckCast(arr, exp, options);
+  };
+
+  //    check same type passed on to casting
+  check_cast(dictionary(int8(), int16()), dictionary(int8(), int16()),
+             "[1, 2, 3, 1, null, 3]");
+  check_cast(dictionary(int8(), int16()), dictionary(int32(), int64()),
+             "[1, 2, 3, 1, null, 3]");
+  check_cast(dictionary(int32(), utf8()), dictionary(int8(), utf8()),
+             R"(["a", "b", "a", null])");
+
+  auto arr = ArrayFromJSON(dictionary(int32(), int32()), "[1, 1000]");
+  // check unsafe
+  ASSERT_OK_AND_ASSIGN(auto casted,
+                       Cast(arr, dictionary(int8(), int8()), CastOptions::Unsafe()));
+  ValidateOutput(casted);

Review comment:
       Maybe it's worth individually checking unsafe casts of the index and dictionary type?

##########
File path: cpp/src/arrow/compute/kernels/scalar_cast_dictionary.cc
##########
@@ -0,0 +1,123 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+// Implementation of casting to dictionary type
+
+#include <arrow/util/bitmap_ops.h>
+
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/cast_internal.h"
+#include "arrow/compute/kernels/scalar_cast_internal.h"
+#include "arrow/compute/kernels/util_internal.h"
+#include "arrow/util/int_util.h"
+
+namespace arrow {
+using internal::CopyBitmap;
+
+namespace compute {
+namespace internal {
+
+Status CastDictionary(KernelContext* ctx, const ExecBatch& batch, Datum* out) {
+  const CastOptions& options = CastState::Get(ctx);
+  auto out_type = std::static_pointer_cast<DictionaryType>(out->type());
+
+  // if out type is same as in type, return input
+  if (out_type->Equals(batch[0].type())) {
+    *out = batch[0];
+    return Status::OK();
+  }
+
+  if (batch[0].is_scalar()) {  // if input is scalar
+    auto in_scalar = std::static_pointer_cast<DictionaryScalar>(batch[0].scalar());

Review comment:
       nit: use internal::checked_cast?

##########
File path: cpp/src/arrow/compute/kernels/scalar_cast_dictionary.cc
##########
@@ -0,0 +1,123 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+// Implementation of casting to dictionary type
+
+#include <arrow/util/bitmap_ops.h>
+
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/cast_internal.h"
+#include "arrow/compute/kernels/scalar_cast_internal.h"
+#include "arrow/compute/kernels/util_internal.h"
+#include "arrow/util/int_util.h"
+
+namespace arrow {
+using internal::CopyBitmap;
+
+namespace compute {
+namespace internal {
+
+Status CastDictionary(KernelContext* ctx, const ExecBatch& batch, Datum* out) {
+  const CastOptions& options = CastState::Get(ctx);
+  auto out_type = std::static_pointer_cast<DictionaryType>(out->type());
+
+  // if out type is same as in type, return input
+  if (out_type->Equals(batch[0].type())) {
+    *out = batch[0];
+    return Status::OK();
+  }
+
+  if (batch[0].is_scalar()) {  // if input is scalar
+    auto in_scalar = std::static_pointer_cast<DictionaryScalar>(batch[0].scalar());
+
+    // if invalid scalar, return null scalar
+    if (!in_scalar->is_valid) {
+      *out = MakeNullScalar(out_type);
+      return Status::OK();
+    }
+
+    Datum casted_index, casted_dict;
+    if (in_scalar->value.index->type->Equals(out_type->index_type())) {
+      casted_index = in_scalar->value.index;
+    } else {
+      ARROW_ASSIGN_OR_RAISE(casted_index,
+                            Cast(in_scalar->value.index, out_type->index_type(), options,
+                                 ctx->exec_context()));
+    }
+
+    if (in_scalar->value.dictionary->type()->Equals(out_type->value_type())) {
+      casted_dict = in_scalar->value.dictionary;
+    } else {
+      ARROW_ASSIGN_OR_RAISE(
+          casted_dict, Cast(in_scalar->value.dictionary, out_type->value_type(), options,
+                            ctx->exec_context()));
+    }
+
+    *out = std::static_pointer_cast<Scalar>(
+        DictionaryScalar::Make(casted_index.scalar(), casted_dict.make_array()));
+
+    return Status::OK();
+  }
+
+  // if input is array
+  const std::shared_ptr<ArrayData>& in_array = batch[0].array();
+  auto in_type = std::static_pointer_cast<DictionaryType>(in_array->type);
+
+  ArrayData* out_array = out->mutable_array();
+
+  if (in_type->index_type()->Equals(out_type->index_type())) {
+    out_array->buffers[0] = in_array->buffers[0];
+    out_array->buffers[1] = in_array->buffers[1];
+  } else {
+    // for indices, create a dummy ArrayData with index_type()
+    const std::shared_ptr<ArrayData>& indices_arr =
+        ArrayData::Make(in_type->index_type(), in_array->length, in_array->buffers,
+                        in_array->GetNullCount(), in_array->offset);
+    ARROW_ASSIGN_OR_RAISE(auto casted_indices, Cast(indices_arr, out_type->index_type(),
+                                                    options, ctx->exec_context()));
+    out_array->buffers[0] = std::move(casted_indices.array()->buffers[0]);
+    out_array->buffers[1] = std::move(casted_indices.array()->buffers[1]);
+  }
+
+  // data (dict)
+  if (in_type->index_type()->Equals(out_type->index_type())) {

Review comment:
       Shouldn't this be checking value_type?

##########
File path: cpp/src/arrow/compute/kernels/scalar_cast_dictionary.cc
##########
@@ -0,0 +1,123 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+// Implementation of casting to dictionary type
+
+#include <arrow/util/bitmap_ops.h>
+
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/cast_internal.h"
+#include "arrow/compute/kernels/scalar_cast_internal.h"
+#include "arrow/compute/kernels/util_internal.h"
+#include "arrow/util/int_util.h"
+
+namespace arrow {
+using internal::CopyBitmap;
+
+namespace compute {
+namespace internal {
+
+Status CastDictionary(KernelContext* ctx, const ExecBatch& batch, Datum* out) {
+  const CastOptions& options = CastState::Get(ctx);
+  auto out_type = std::static_pointer_cast<DictionaryType>(out->type());
+
+  // if out type is same as in type, return input
+  if (out_type->Equals(batch[0].type())) {
+    *out = batch[0];
+    return Status::OK();
+  }
+
+  if (batch[0].is_scalar()) {  // if input is scalar
+    auto in_scalar = std::static_pointer_cast<DictionaryScalar>(batch[0].scalar());
+
+    // if invalid scalar, return null scalar
+    if (!in_scalar->is_valid) {
+      *out = MakeNullScalar(out_type);
+      return Status::OK();
+    }
+
+    Datum casted_index, casted_dict;
+    if (in_scalar->value.index->type->Equals(out_type->index_type())) {
+      casted_index = in_scalar->value.index;
+    } else {
+      ARROW_ASSIGN_OR_RAISE(casted_index,
+                            Cast(in_scalar->value.index, out_type->index_type(), options,
+                                 ctx->exec_context()));
+    }
+
+    if (in_scalar->value.dictionary->type()->Equals(out_type->value_type())) {
+      casted_dict = in_scalar->value.dictionary;
+    } else {
+      ARROW_ASSIGN_OR_RAISE(
+          casted_dict, Cast(in_scalar->value.dictionary, out_type->value_type(), options,
+                            ctx->exec_context()));
+    }
+
+    *out = std::static_pointer_cast<Scalar>(
+        DictionaryScalar::Make(casted_index.scalar(), casted_dict.make_array()));
+
+    return Status::OK();
+  }
+
+  // if input is array
+  const std::shared_ptr<ArrayData>& in_array = batch[0].array();
+  auto in_type = std::static_pointer_cast<DictionaryType>(in_array->type);
+
+  ArrayData* out_array = out->mutable_array();
+
+  if (in_type->index_type()->Equals(out_type->index_type())) {
+    out_array->buffers[0] = in_array->buffers[0];
+    out_array->buffers[1] = in_array->buffers[1];

Review comment:
       What if there's an offset? I suppose it does pass CheckCast which does do slicing…

##########
File path: cpp/src/arrow/compute/kernels/scalar_cast_dictionary.cc
##########
@@ -0,0 +1,123 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+// Implementation of casting to dictionary type
+
+#include <arrow/util/bitmap_ops.h>
+
+#include "arrow/array/builder_primitive.h"
+#include "arrow/compute/cast_internal.h"
+#include "arrow/compute/kernels/scalar_cast_internal.h"
+#include "arrow/compute/kernels/util_internal.h"
+#include "arrow/util/int_util.h"
+
+namespace arrow {
+using internal::CopyBitmap;
+
+namespace compute {
+namespace internal {
+
+Status CastDictionary(KernelContext* ctx, const ExecBatch& batch, Datum* out) {
+  const CastOptions& options = CastState::Get(ctx);
+  auto out_type = std::static_pointer_cast<DictionaryType>(out->type());
+
+  // if out type is same as in type, return input
+  if (out_type->Equals(batch[0].type())) {
+    *out = batch[0];
+    return Status::OK();
+  }
+
+  if (batch[0].is_scalar()) {  // if input is scalar
+    auto in_scalar = std::static_pointer_cast<DictionaryScalar>(batch[0].scalar());
+
+    // if invalid scalar, return null scalar
+    if (!in_scalar->is_valid) {
+      *out = MakeNullScalar(out_type);
+      return Status::OK();
+    }
+
+    Datum casted_index, casted_dict;
+    if (in_scalar->value.index->type->Equals(out_type->index_type())) {
+      casted_index = in_scalar->value.index;
+    } else {
+      ARROW_ASSIGN_OR_RAISE(casted_index,
+                            Cast(in_scalar->value.index, out_type->index_type(), options,
+                                 ctx->exec_context()));
+    }
+
+    if (in_scalar->value.dictionary->type()->Equals(out_type->value_type())) {
+      casted_dict = in_scalar->value.dictionary;
+    } else {
+      ARROW_ASSIGN_OR_RAISE(
+          casted_dict, Cast(in_scalar->value.dictionary, out_type->value_type(), options,
+                            ctx->exec_context()));
+    }
+
+    *out = std::static_pointer_cast<Scalar>(
+        DictionaryScalar::Make(casted_index.scalar(), casted_dict.make_array()));
+
+    return Status::OK();
+  }
+
+  // if input is array
+  const std::shared_ptr<ArrayData>& in_array = batch[0].array();
+  auto in_type = std::static_pointer_cast<DictionaryType>(in_array->type);
+
+  ArrayData* out_array = out->mutable_array();
+
+  if (in_type->index_type()->Equals(out_type->index_type())) {
+    out_array->buffers[0] = in_array->buffers[0];
+    out_array->buffers[1] = in_array->buffers[1];

Review comment:
       It would also be nice to copy null_count.

##########
File path: cpp/src/arrow/CMakeLists.txt
##########
@@ -385,7 +385,8 @@ if(ARROW_COMPUTE)
        compute/kernels/scalar_arithmetic.cc
        compute/kernels/scalar_boolean.cc
        compute/kernels/scalar_cast_boolean.cc
-       compute/kernels/scalar_cast_internal.cc
+          compute/kernels/scalar_cast_dictionary.cc
+          compute/kernels/scalar_cast_internal.cc

Review comment:
       nit: this needs to be cmake-formatted




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