[GitHub] [arrow] jorisvandenbossche commented on pull request #8271: ARROW-9991: [C++] split kernels for strings/binary

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

jorisvandenbossche commented on pull request #8271:
URL: https://github.com/apache/arrow/pull/8271#issuecomment-701380049


   > This also raised a question: Should both the list entry and the string array entry have a missing/null value if the input string contains a null value? I think it should because if we ask for the underlying string array, and the string value that the missing list entry points to is not a missing value, it will be an empty string, which seems odd to me.
   
   Buf if the original string was a null, then the output also contains a (top-level) null, and not a list with a null?
   
   And then such top-level nulls are typically not put as an entry in the actual values array (or at least when arrow is building up a list array itself, the format might also not allow otherwise). Eg:
   
   ```
   In [10]: arr = pa.array([["a", "b"], None, ["c"], [None]])
   
   In [11]: arr
   Out[11]: 
   <pyarrow.lib.ListArray object at 0x7f2316c1d108>
   [
     [
       "a",
       "b"
     ],
     null,
     [
       "c"
     ],
     [
       null
     ]
   ]
   
   In [12]: arr.values
   Out[12]: 
   <pyarrow.lib.StringArray object at 0x7f2316c1d5e8>
   [
     "a",
     "b",
     "c",
     null
   ]
   ```
   
   (so only the null that was inside a list is represented as null in the underlying values array)


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