[GitHub] [arrow] edponce commented on a diff in pull request #11115: ARROW-12084: [C++][Compute] Add remainder and quotient compute::Function

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

edponce commented on code in PR #11115:
URL: https://github.com/apache/arrow/pull/11115#discussion_r924585304


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cpp/src/arrow/compute/kernels/scalar_arithmetic.cc:
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@@ -1001,6 +1001,95 @@ struct Trunc {
   }
 };
 
+// TODO(edponce): Move builders to function state and reset.
+struct Divmod {
+  template <typename T, typename Arg0, typename Arg1>
+  static enable_if_floating_value<T, FixedSizeListScalar> Call(KernelContext* ctx, Arg0 dividend, Arg1 divisor, Status* st) {
+    T quotient = std::floor(dividend / divisor);
+    T remainder = dividend - quotient * divisor;
+
+    NumericBuilder<T> builder;
+    builder.Append(quotient);
+    builder.Append(remainder);
+    std::shared_ptr<Array> array;
+    builder.Finish(&array);
+    FixedSizeListScalar list(array, builder.type())

Review Comment:
   I know, although we can cache the builder but still need to create the `FixedSizeListScalar`. I have not found a reasonable solution for the output of this kernel or more generally:
   **What scalar and array types to use for a kernel that outputs multiple values?**
   Any suggestions on how to return a pair of values (same type) from a kernel?
   cc @pitrou 
   
   Ideas:
   * Return an Array that is twice as large - drawback is that output indices are of the form: `2i, 2i+1`
   * Return a `StructArray` or `MapArray` - require a key-value pair during construction, these structures support different value types
   * Return a `FixedSizeListArray`



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