[GitHub] [arrow] nirandaperera commented on a change in pull request #11886: ARROW-13035: [C++] nonzero compute function

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

nirandaperera commented on a change in pull request #11886:
URL: https://github.com/apache/arrow/pull/11886#discussion_r764325585



##########
File path: cpp/src/arrow/compute/kernels/scalar_validity.cc
##########
@@ -189,6 +191,72 @@ Status ConstBoolExec(KernelContext* ctx, const ExecBatch& batch, Datum* out) {
   return Status::OK();
 }
 
+struct NonZeroVisitor {
+   UInt32Builder *builder;
+   const ArrayData& array;
+
+   NonZeroVisitor(UInt32Builder *builder, const ArrayData& array)
+   : builder(builder), array(array) {}
+
+  Status Visit(const DataType& type) {
+    return Status::TypeError("Unsupported type for nonzero: ", type.ToString());
+  }
+
+   template <typename Type> 
+   enable_if_t<has_c_type<Type>::value && 
+              !std::is_same<Type, MonthDayNanoIntervalType>::value &&
+              !std::is_same<Type, DayTimeIntervalType>::value, 
+              Status>
+   Visit(const Type&) {
+     using T = typename GetViewType<Type>::T;
+     uint32_t index = 0;
+
+     return VisitArrayDataInline<Type>(
+        this->array,
+        [&](T v) {
+          if(v != 0) {
+            RETURN_NOT_OK(this->builder->Reserve(1));
+            this->builder->UnsafeAppend(index);

Review comment:
       @edponce that would be quite slow, isn't it? I think builder should reserve initially to array length and then do unsafeappend 




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