[GitHub] [arrow] mbrobbel commented on a change in pull request #11937: ARROW-1569: [C++] Kernel functions for determining monotonicity (ascending or descending) for well-ordered types

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

mbrobbel commented on a change in pull request #11937:
URL: https://github.com/apache/arrow/pull/11937#discussion_r771264722



##########
File path: cpp/src/arrow/compute/kernels/vector_is_monotonic.cc
##########
@@ -0,0 +1,321 @@
+// 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 "arrow/compute/api_vector.h"
+#include "arrow/compute/kernel.h"
+#include "arrow/compute/kernels/aggregate_internal.h"
+#include "arrow/compute/registry.h"
+#include "arrow/util/optional.h"
+
+namespace arrow {
+namespace compute {
+namespace internal {
+
+namespace {
+// ----------------------------------------------------------------------
+// IsMonotonic implementation
+
+using IsMonotonicState = OptionsWrapper<IsMonotonicOptions>;
+
+Status IsMonotonicOutput(bool increasing, bool strictly_increasing, bool decreasing,
+                         bool strictly_decreasing, Datum* out) {
+  ARROW_ASSIGN_OR_RAISE(
+      *out, StructScalar::Make({std::make_shared<BooleanScalar>(increasing),
+                                std::make_shared<BooleanScalar>(strictly_increasing),
+                                std::make_shared<BooleanScalar>(decreasing),
+                                std::make_shared<BooleanScalar>(strictly_decreasing)},
+                               {"increasing", "strictly_increasing", "decreasing",
+                                "strictly_decreasing"}));
+  return Status::OK();
+}
+
+template <typename DataType>
+enable_if_floating_point<DataType> IsMonotonicCheck(
+    const typename DataType::c_type& current, const typename DataType::c_type& next,
+    bool* increasing, bool* strictly_increasing, bool* decreasing,
+    bool* strictly_decreasing, const IsMonotonicOptions& options) {
+  // Short circuit for NaNs.
+  // https://en.wikipedia.org/wiki/NaN#Comparison_with_NaN
+  if (std::isnan(current) || std::isnan(next)) {
+    *increasing = false;
+    *strictly_increasing = false;
+    *decreasing = false;
+    *strictly_decreasing = false;
+  } else {
+    bool equal =
+        // Approximately equal within some error bound (epsilon).
+        (options.floating_approximate &&
+         (fabs(current - next) <=
+          static_cast<typename DataType::c_type>(options.epsilon))) ||
+        // Or exactly equal.
+        current == next;
+    if (*increasing) {
+      if (!(equal || next > current)) {
+        *increasing = false;
+        *strictly_increasing = false;
+      }
+    }
+    if (*decreasing) {
+      if (!(equal || next < current)) {
+        *decreasing = false;
+        *strictly_decreasing = false;
+      }
+    }
+    if (*strictly_increasing) {
+      if (equal || !(next > current)) {
+        *strictly_increasing = false;
+      }
+    }
+    if (*strictly_decreasing) {
+      if (equal || !(next < current)) {
+        *strictly_decreasing = false;
+      }
+    }
+  }
+}
+
+template <typename DataType>
+enable_if_not_floating_point<DataType> IsMonotonicCheck(
+    const typename DataType::c_type& current, const typename DataType::c_type& next,
+    bool* increasing, bool* strictly_increasing, bool* decreasing,
+    bool* strictly_decreasing, const IsMonotonicOptions& options) {
+  if (*increasing) {
+    if (!(next >= current)) {
+      *increasing = false;
+      *strictly_increasing = false;
+    }
+  }
+  if (*strictly_increasing) {
+    if (!(next > current)) {
+      *strictly_increasing = false;
+    }
+  }
+  if (*decreasing) {
+    if (!(next <= current)) {
+      *decreasing = false;
+      *strictly_decreasing = false;
+    }
+  }
+  if (*strictly_decreasing) {
+    if (!(next < current)) {
+      *strictly_decreasing = false;
+    }
+  }
+}
+
+template <typename DataType>
+enable_if_floating_point<DataType, bool> isnan(
+    const util::optional<typename DataType::c_type>& opt) {
+  return opt.has_value() && std::isnan(opt.value());
+}
+
+template <typename DataType>
+enable_if_not_floating_point<DataType, bool> isnan(
+    const util::optional<typename DataType::c_type>& opt) {
+  return false;
+}
+
+template <typename DataType>
+constexpr enable_if_floating_point<DataType, typename DataType::c_type> min() {
+  return -std::numeric_limits<typename DataType::c_type>::infinity();
+}
+
+template <typename DataType>
+constexpr enable_if_floating_point<DataType, typename DataType::c_type> max() {
+  return std::numeric_limits<typename DataType::c_type>::infinity();
+}
+
+template <typename DataType>
+constexpr enable_if_not_floating_point<DataType, typename DataType::c_type> min() {
+  return std::numeric_limits<typename DataType::c_type>::min();
+}
+
+template <typename DataType>
+constexpr enable_if_not_floating_point<DataType, typename DataType::c_type> max() {
+  return std::numeric_limits<typename DataType::c_type>::max();
+}
+
+template <typename DataType>
+Status IsMonotonic(KernelContext* ctx, const ExecBatch& batch, Datum* out) {
+  using ArrayType = typename TypeTraits<DataType>::ArrayType;
+  using CType = typename TypeTraits<DataType>::CType;
+
+  auto options = IsMonotonicState::Get(ctx);
+
+  // Check batch size
+  if (batch.values.size() != 1) {

Review comment:
       Directly invocation of this kernel is not possible through the public API, however internally this function could be invoked directly and skip those checks. @bkietz what do you suggest?




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