[jira] [Created] (ARROW-6042) [C++] Implement alternative DictionaryBuilder that always yields int32 indices

["Wes McKinney (JIRA)" <ji...@apache.org>]

Wes McKinney created ARROW-6042:
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             Summary: [C++] Implement alternative DictionaryBuilder that always yields int32 indices
                 Key: ARROW-6042
                 URL: https://issues.apache.org/jira/browse/ARROW-6042
             Project: Apache Arrow
          Issue Type: Improvement
          Components: C++
            Reporter: Wes McKinney
             Fix For: 1.0.0


One problem with the current {{DictionaryBuilder<T>}} in some applications is that, if it is used to produce a series of arrays to form a ChunkedArray, it may yield constituent chunks having different index widths. For example:

{code}
chunk 0: int8 indices
chunk 1: int16 indices
chunk 2: int16 indices
chunk 3: int32 indices
chunk 4: int32 indices
chunk 5: int32 indices
chunk 6: int32 indices
{code}

Obviously this is problematic for these applications. I'm running into this issue in the context of ARROW-3772 where we are looking to decode Parquet data directly to {{DictionaryArray}} without stepping through an intermediate dense decoded stage. 

I'm not sure what to call the class, whether {{DictionaryInt32Builder}} or something similar, but this would be the same API more or less as {{DictionaryBuilder}} but instead use {{Int32Builder}} for the indices rather than {{AdaptiveIntBuilder}}.



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