ARROW-13390: [C++] Implement coalesce for remaining types

c_glib/test/test-dense-union-scalar.rb

@@ -49,7 +49,7 @@ def test_equal
   end
 
   def test_to_s
-    assert_equal("...", @scalar.to_s)
+    assert_equal("union{number: int8 = -29}", @scalar.to_s)
   end
 
   def test_value

c_glib/test/test-sparse-union-scalar.rb

@@ -49,7 +49,7 @@ def test_equal
   end
 
   def test_to_s
-    assert_equal("...", @scalar.to_s)
+    assert_equal("union{number: int8 = -29}", @scalar.to_s)
   end
 
   def test_value

cpp/src/arrow/compute/kernels/CMakeLists.txt

@@ -71,3 +71,8 @@ add_arrow_compute_test(aggregate_test
                        hash_aggregate_test.cc
                        test_util.cc)
 add_arrow_benchmark(aggregate_benchmark PREFIX "arrow-compute")
+
+# ----------------------------------------------------------------------
+# Utilities
+
+add_arrow_compute_test(kernel_utility_test SOURCES codegen_internal_test.cc)

cpp/src/arrow/compute/kernels/codegen_internal.cc

@@ -95,8 +95,14 @@ void ReplaceNullWithOtherType(std::vector<ValueDescr>* descrs) {
 
 void ReplaceTypes(const std::shared_ptr<DataType>& type,
                   std::vector<ValueDescr>* descrs) {
-  for (auto& descr : *descrs) {
-    descr.type = type;
+  ReplaceTypes(type, descrs->data(), descrs->size());
+}
+
+void ReplaceTypes(const std::shared_ptr<DataType>& type, ValueDescr* begin,
+                  size_t count) {
+  auto* end = begin + count;
+  for (auto* it = begin; it != end; it++) {
+    it->type = type;
   }
 }
 
@@ -158,26 +164,47 @@ std::shared_ptr<DataType> CommonNumeric(const ValueDescr* begin, size_t count) {
   return int8();
 }
 
-std::shared_ptr<DataType> CommonTimestamp(const std::vector<ValueDescr>& descrs) {
+std::shared_ptr<DataType> CommonTemporal(const std::vector<ValueDescr>& descrs) {
   TimeUnit::type finest_unit = TimeUnit::SECOND;
+  const std::string* timezone = nullptr;
+  bool saw_date32 = false;
+  bool saw_date64 = false;
 
   for (const auto& descr : descrs) {
     auto id = descr.type->id();
     // a common timestamp is only possible if all types are timestamp like
     switch (id) {
       case Type::DATE32:
+        // Date32's unit is days, but the coarsest we have is seconds
+        saw_date32 = true;
+        continue;
       case Type::DATE64:
+        finest_unit = std::max(finest_unit, TimeUnit::MILLI);
+        saw_date64 = true;
         continue;
-      case Type::TIMESTAMP:
-        finest_unit =
-            std::max(finest_unit, checked_cast<const TimestampType&>(*descr.type).unit());
+      case Type::TIMESTAMP: {
+        const auto& ty = checked_cast<const TimestampType&>(*descr.type);
+        // Don't cast to common timezone by default (may not make
+        // sense for all kernels)
+        if (timezone && *timezone != ty.timezone()) return nullptr;
+        timezone = &ty.timezone();
+        finest_unit = std::max(finest_unit, ty.unit());
         continue;
+      }
       default:
         return nullptr;
     }
   }
 
-  return timestamp(finest_unit);
+  if (timezone) {
+    // At least one timestamp seen
+    return timestamp(finest_unit, *timezone);
+  } else if (saw_date64) {
+    return date64();
+  } else if (saw_date32) {
+    return date32();
+  }
+  return nullptr;
 }
 
 std::shared_ptr<DataType> CommonBinary(const std::vector<ValueDescr>& descrs) {
@@ -290,6 +317,67 @@ Status CastBinaryDecimalArgs(DecimalPromotion promotion,
   return Status::OK();
 }
 
+Status CastDecimalArgs(ValueDescr* begin, size_t count) {
+  Type::type casted_type_id = Type::DECIMAL128;
+  auto* end = begin + count;
+
+  int32_t max_scale = 0;
+  bool any_floating = false;
+  for (auto* it = begin; it != end; ++it) {
+    const auto& ty = *it->type;
+    if (is_floating(ty.id())) {
+      // Decimal + float = float
+      any_floating = true;
+    } else if (is_integer(ty.id())) {
+      // Nothing to do here
+    } else if (is_decimal(ty.id())) {
+      max_scale = std::max(max_scale, checked_cast<const DecimalType&>(ty).scale());
+      if (ty.id() == Type::DECIMAL256) {
+        casted_type_id = Type::DECIMAL256;
+      }
+    } else {
+      // Non-numeric, can't cast
+      return Status::OK();
+    }
+  }
+  if (any_floating) {
+    ReplaceTypes(float64(), begin, count);
+    return Status::OK();
+  }
+
+  // All integer and decimal, rescale
+  int32_t common_precision = 0;
+  for (auto* it = begin; it != end; ++it) {
+    const auto& ty = *it->type;
+    if (is_integer(ty.id())) {
+      ARROW_ASSIGN_OR_RAISE(auto precision, MaxDecimalDigitsForInteger(ty.id()));
+      precision += max_scale;
+      common_precision = std::max(common_precision, precision);
+    } else if (is_decimal(ty.id())) {
+      const auto& decimal_ty = checked_cast<const DecimalType&>(ty);
+      auto precision = decimal_ty.precision();
+      const auto scale = decimal_ty.scale();
+      precision += max_scale - scale;
+      common_precision = std::max(common_precision, precision);
+    }
+  }
+
+  if (common_precision > BasicDecimal256::kMaxPrecision) {
+    return Status::Invalid("Result precision (", common_precision,
+                           ") exceeds max precision of Decimal256 (",
+                           BasicDecimal256::kMaxPrecision, ")");
+  } else if (common_precision > BasicDecimal128::kMaxPrecision) {
+    casted_type_id = Type::DECIMAL256;
+  }
+
+  for (auto* it = begin; it != end; ++it) {
+    ARROW_ASSIGN_OR_RAISE(it->type,
+                          DecimalType::Make(casted_type_id, common_precision, max_scale));
+  }
+
+  return Status::OK();
+}
+
 bool HasDecimal(const std::vector<ValueDescr>& descrs) {
   for (const auto& descr : descrs) {
     if (is_decimal(descr.type->id())) {

cpp/src/arrow/compute/kernels/codegen_internal.h

@@ -1279,14 +1279,17 @@ void ReplaceNullWithOtherType(std::vector<ValueDescr>* descrs);
 ARROW_EXPORT
 void ReplaceTypes(const std::shared_ptr<DataType>&, std::vector<ValueDescr>* descrs);
 
+ARROW_EXPORT
+void ReplaceTypes(const std::shared_ptr<DataType>&, ValueDescr* descrs, size_t count);
+
 ARROW_EXPORT
 std::shared_ptr<DataType> CommonNumeric(const std::vector<ValueDescr>& descrs);
 
 ARROW_EXPORT
 std::shared_ptr<DataType> CommonNumeric(const ValueDescr* begin, size_t count);
 
 ARROW_EXPORT
-std::shared_ptr<DataType> CommonTimestamp(const std::vector<ValueDescr>& descrs);
+std::shared_ptr<DataType> CommonTemporal(const std::vector<ValueDescr>& descrs);
 
 ARROW_EXPORT
 std::shared_ptr<DataType> CommonBinary(const std::vector<ValueDescr>& descrs);
@@ -1298,9 +1301,17 @@ enum class DecimalPromotion : uint8_t {
   kDivide,
 };
 
+/// Given two arguments, at least one of which is decimal, promote all
+/// to not necessarily identical types, but types which are compatible
+/// for the given operator (add/multiply/divide).
 ARROW_EXPORT
 Status CastBinaryDecimalArgs(DecimalPromotion promotion, std::vector<ValueDescr>* descrs);
 
+/// Given one or more arguments, at least one of which is decimal,
+/// promote all to an identical type.
+ARROW_EXPORT
+Status CastDecimalArgs(ValueDescr* begin, size_t count);
+
 ARROW_EXPORT
 bool HasDecimal(const std::vector<ValueDescr>& descrs);
 

cpp/src/arrow/compute/kernels/codegen_internal_test.cc

@@ -0,0 +1,155 @@
+// 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.
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+
+#include "arrow/compute/kernels/codegen_internal.h"
+#include "arrow/testing/gtest_util.h"
+#include "arrow/type.h"
+#include "arrow/type_fwd.h"
+
+namespace arrow {
+namespace compute {
+namespace internal {
+
+TEST(TestDispatchBest, CastBinaryDecimalArgs) {
+  std::vector<ValueDescr> args;
+  std::vector<DecimalPromotion> modes = {
+      DecimalPromotion::kAdd, DecimalPromotion::kMultiply, DecimalPromotion::kDivide};
+
+  // Any float -> all float
+  for (auto mode : modes) {
+    args = {decimal128(3, 2), float64()};
+    ASSERT_OK(CastBinaryDecimalArgs(mode, &args));
+    AssertTypeEqual(args[0].type, float64());
+    AssertTypeEqual(args[1].type, float64());
+  }
+
+  // Integer -> decimal with common scale
+  args = {decimal128(1, 0), int64()};
+  ASSERT_OK(CastBinaryDecimalArgs(DecimalPromotion::kAdd, &args));
+  AssertTypeEqual(args[0].type, decimal128(1, 0));
+  AssertTypeEqual(args[1].type, decimal128(19, 0));
+
+  // Add: rescale so all have common scale
+  args = {decimal128(3, 2), decimal128(3, -2)};
+  EXPECT_RAISES_WITH_MESSAGE_THAT(
+      NotImplemented, ::testing::HasSubstr("Decimals with negative scales not supported"),
+      CastBinaryDecimalArgs(DecimalPromotion::kAdd, &args));
+}
+
+TEST(TestDispatchBest, CastDecimalArgs) {
+  std::vector<ValueDescr> args;
+
+  // Any float -> all float
+  args = {decimal128(3, 2), float64()};
+  ASSERT_OK(CastDecimalArgs(args.data(), args.size()));
+  AssertTypeEqual(args[0].type, float64());
+  AssertTypeEqual(args[1].type, float64());
+
+  args = {float32(), float64(), decimal128(3, 2)};
+  ASSERT_OK(CastDecimalArgs(args.data(), args.size()));
+  AssertTypeEqual(args[0].type, float64());
+  AssertTypeEqual(args[1].type, float64());
+  AssertTypeEqual(args[2].type, float64());
+
+  // Promote to common decimal width
+  args = {decimal128(3, 2), decimal256(3, 2)};
+  ASSERT_OK(CastDecimalArgs(args.data(), args.size()));
+  AssertTypeEqual(args[0].type, decimal256(3, 2));
+  AssertTypeEqual(args[1].type, decimal256(3, 2));
+
+  // Rescale so all have common scale/precision
+  args = {decimal128(3, 2), decimal128(3, 0)};
+  ASSERT_OK(CastDecimalArgs(args.data(), args.size()));
+  AssertTypeEqual(args[0].type, decimal128(5, 2));
+  AssertTypeEqual(args[1].type, decimal128(5, 2));
+
+  args = {decimal128(3, 2), decimal128(3, -2)};
+  ASSERT_OK(CastDecimalArgs(args.data(), args.size()));
+  AssertTypeEqual(args[0].type, decimal128(7, 2));
+  AssertTypeEqual(args[1].type, decimal128(7, 2));
+
+  args = {decimal128(3, 0), decimal128(3, 1), decimal128(3, 2)};
+  ASSERT_OK(CastDecimalArgs(args.data(), args.size()));
+  AssertTypeEqual(args[0].type, decimal128(5, 2));
+  AssertTypeEqual(args[1].type, decimal128(5, 2));
+  AssertTypeEqual(args[2].type, decimal128(5, 2));
+
+  // Integer -> decimal with appropriate precision
+  args = {decimal128(3, 0), int64()};
+  ASSERT_OK(CastDecimalArgs(args.data(), args.size()));
+  AssertTypeEqual(args[0].type, decimal128(19, 0));
+  AssertTypeEqual(args[1].type, decimal128(19, 0));
+
+  args = {decimal128(3, 1), int64()};
+  ASSERT_OK(CastDecimalArgs(args.data(), args.size()));
+  AssertTypeEqual(args[0].type, decimal128(20, 1));
+  AssertTypeEqual(args[1].type, decimal128(20, 1));
+
+  args = {decimal128(3, -1), int64()};
+  ASSERT_OK(CastDecimalArgs(args.data(), args.size()));
+  AssertTypeEqual(args[0].type, decimal128(19, 0));
+  AssertTypeEqual(args[1].type, decimal128(19, 0));
+
+  // Overflow decimal128 max precision -> promote to decimal256
+  args = {decimal128(38, 0), decimal128(37, 2)};
+  ASSERT_OK(CastDecimalArgs(args.data(), args.size()));
+  AssertTypeEqual(args[0].type, decimal256(40, 2));
+  AssertTypeEqual(args[1].type, decimal256(40, 2));
+
+  // Overflow decimal256 max precision
+  args = {decimal256(76, 0), decimal256(75, 1)};
+  EXPECT_RAISES_WITH_MESSAGE_THAT(
+      Invalid,
+      ::testing::HasSubstr(
+          "Result precision (77) exceeds max precision of Decimal256 (76)"),
+      CastDecimalArgs(args.data(), args.size()));
+
+  // Incompatible, no cast
+  args = {decimal256(3, 2), float64(), utf8()};
+  ASSERT_OK(CastDecimalArgs(args.data(), args.size()));
+  AssertTypeEqual(args[0].type, decimal256(3, 2));
+  AssertTypeEqual(args[1].type, float64());
+  AssertTypeEqual(args[2].type, utf8());
+}
+
+TEST(TestDispatchBest, CommonTemporal) {
+  AssertTypeEqual(timestamp(TimeUnit::NANO), CommonTemporal({timestamp(TimeUnit::SECOND),
+                                                             timestamp(TimeUnit::NANO)}));
+  AssertTypeEqual(timestamp(TimeUnit::NANO, "UTC"),
+                  CommonTemporal({timestamp(TimeUnit::SECOND, "UTC"),
+                                  timestamp(TimeUnit::NANO, "UTC")}));
+  AssertTypeEqual(timestamp(TimeUnit::NANO),
+                  CommonTemporal({date32(), timestamp(TimeUnit::NANO)}));
+  AssertTypeEqual(timestamp(TimeUnit::MILLI),
+                  CommonTemporal({date64(), timestamp(TimeUnit::SECOND)}));
+  AssertTypeEqual(date32(), CommonTemporal({date32(), date32()}));
+  AssertTypeEqual(date64(), CommonTemporal({date64(), date64()}));
+  AssertTypeEqual(date64(), CommonTemporal({date32(), date64()}));
+  ASSERT_EQ(nullptr, CommonTemporal({}));
+  ASSERT_EQ(nullptr, CommonTemporal({float64(), int32()}));
+  ASSERT_EQ(nullptr, CommonTemporal({timestamp(TimeUnit::SECOND),
+                                     timestamp(TimeUnit::SECOND, "UTC")}));
+  ASSERT_EQ(nullptr, CommonTemporal({timestamp(TimeUnit::SECOND, "America/Phoenix"),
+                                     timestamp(TimeUnit::SECOND, "UTC")}));
+}
+
+}  // namespace internal
+}  // namespace compute
+}  // namespace arrow