andishgar opened a new issue, #50509: URL: https://github.com/apache/arrow/issues/50509
### Describe the enhancement requested `ArrayBuilder::AppendEmptyValue()` was introduced and implemented in [ARROW-25393](https://github.com/apache/arrow/issues/25393) to write an arbitrary, well-defined value during `StructBuilder::AppendNull()`, as discussed [here](https://github.com/apache/arrow/pull/7887#discussion_r470062219). In that context, the value written to the child builder is irrelevant because the parent entry is null. At that time, `RunEndEncodedBuilder` did not yet exist; it was implemented about three years later in [ARROW-32688](https://github.com/apache/arrow/issues/32688). As a result, the current implementation does not appear to consider that the value written by `AppendEmptyValue()` may later become part of the value stream observed by `RunEndEncodedBuilder`. this can be problematic for RunEndEncodedBuilder with floating-point values, as it can produce a zero value, which cannot be considered an empty value (Case 1). Even worse, it can be mistakenly confused with actual floating-point values (see the example below). ### Case 1 ```c++ auto ree_type = run_end_encoded(int32(), float32()); auto int32_builder = std::make_shared<Int32Builder>(pool_); auto float_builder = std::make_shared<FloatBuilder>(pool_); RunEndEncodedBuilder builder(pool_, int32_builder, float_builder, ree_type); ASSERT_OK(builder.AppendEmptyValues(3)); ASSERT_OK(builder.AppendScalar(**MakeScalar(float32(), 3), 3)); ASSERT_OK_AND_ASSIGN(auto array, builder.Finish()); ARROW_LOGGER_INFO("", array->ToString()); ``` Output: ```text -- run_ends: [ 3, 6 ] -- values: [ 0, 3 ] ``` ### Case 2 ```c++ auto ree_type = run_end_encoded(int32(), float32()); auto int32_builder = std::make_shared<Int32Builder>(pool_); auto float_builder = std::make_shared<FloatBuilder>(pool_); RunEndEncodedBuilder builder(pool_, int32_builder, float_builder, ree_type); ASSERT_OK(builder.AppendEmptyValues(3)); ASSERT_OK(builder.AppendScalar(**MakeScalar(float32(), 0), 3)); ASSERT_OK_AND_ASSIGN(auto array, builder.Finish()); ARROW_LOGGER_INFO("", array->ToString()); ``` Output: ```text -- run_ends: [ 3, 6 ] -- values: [ 0, 0 ] ``` One possible solution would be to use `NaN` as the placeholder value for floating-point builders instead of `0.0f`. ### Component(s) C++ -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
