[jira] [Created] (ARROW-6923) [C++] Option for Filter kernel how to handle nulls in the selection vector

["Joris Van den Bossche (Jira)" <ji...@apache.org>]

Joris Van den Bossche created ARROW-6923:
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             Summary: [C++] Option for Filter kernel how to handle nulls in the selection vector
                 Key: ARROW-6923
                 URL: https://issues.apache.org/jira/browse/ARROW-6923
             Project: Apache Arrow
          Issue Type: Improvement
          Components: C++
            Reporter: Joris Van den Bossche


How nulls are handled in the boolean mask (selection vector) in a filter kernel varies between languages / data analytics systems (e.g. base R propagates nulls, dplyr R skips (sees as False), SQL generally skips them as well I think, Julia raises an error).

Currently, in Arrow C++ we "propagate" nulls (null in the selection vector gives a null in the output):

{code}
In [7]: arr = pa.array([1, 2, 3]) 

In [8]: mask = pa.array([True, False, None]) 

In [9]: arr.filter(mask) 
Out[9]: 
<pyarrow.lib.Int64Array object at 0x7fefe44b3048>
[
  1,
  null
]
{code}

Given the different ways this could be done (propagate, skip, error), should we provide an option to control this behaviour?



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