[GitHub] [arrow] lidavidm commented on a change in pull request #10390: ARROW-12751: [C++] Implement minimum/maximum kernels

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

lidavidm commented on a change in pull request #10390:
URL: https://github.com/apache/arrow/pull/10390#discussion_r643232604



##########
File path: cpp/src/arrow/compute/kernels/scalar_arithmetic.cc
##########
@@ -516,6 +564,190 @@ std::shared_ptr<ScalarFunction> MakeUnarySignedArithmeticFunctionNotNull(
   return func;
 }
 
+using MinMaxState = OptionsWrapper<ElementWiseAggregateOptions>;
+
+// Implement a variadic scalar min/max kernel.
+template <typename OutType, typename Op>
+struct ScalarMinMax {
+  using OutValue = typename GetOutputType<OutType>::T;
+
+  static void ExecScalar(const ExecBatch& batch,
+                         const ElementWiseAggregateOptions& options, Scalar* out) {
+    // All arguments are scalar
+    OutValue value{};
+    bool valid = false;
+    for (const auto& arg : batch.values) {
+      // Ignore non-scalar arguments so we can use it in the mixed-scalar-and-array case
+      if (!arg.is_scalar()) continue;
+      const auto& scalar = *arg.scalar();
+      if (!scalar.is_valid) {
+        if (options.skip_nulls) continue;
+        out->is_valid = false;
+        return;
+      }
+      if (!valid) {
+        value = UnboxScalar<OutType>::Unbox(scalar);
+        valid = true;
+      } else {
+        value = Op::Call(value, UnboxScalar<OutType>::Unbox(scalar));
+      }
+    }
+    out->is_valid = valid;
+    if (valid) {
+      BoxScalar<OutType>::Box(value, out);
+    }
+  }
+
+  static Status Exec(KernelContext* ctx, const ExecBatch& batch, Datum* out) {
+    const ElementWiseAggregateOptions& options = MinMaxState::Get(ctx);
+    const auto descrs = batch.GetDescriptors();
+    const size_t scalar_count =
+        static_cast<size_t>(std::count_if(batch.values.begin(), batch.values.end(),
+                                          [](const Datum& d) { return d.is_scalar(); }));
+    if (scalar_count == batch.values.size()) {
+      ExecScalar(batch, options, out->scalar().get());
+      return Status::OK();
+    }
+
+    ArrayData* output = out->mutable_array();

Review comment:
       This works quite well except in the case that we have a singular NaN array argument (`element_wise_min([NaN])`) - in which case we want to emit `NaN` not the antiextreme.




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