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  1. Apache Arrow
  2. ARROW-7266

[Python] dictionary_encode() of a slice gives wrong result

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Details

    • Bug
    • Status: Resolved
    • Major
    • Resolution: Fixed
    • 0.15.1
    • 0.16.0
    • C++, Python
    • Docker on Linux 5.2.18-200.fc30.x86_64; Python 3.7.4

    Description

      Steps to reproduce:

      import pyarrow as pa
      arr = pa.array(["a", "b", "b", "b"])[1:]
      arr.dictionary_encode()
      

      Expected results:

      -- dictionary:
        [
          "b"
        ]
      -- indices:
        [
          0,
          0,
          0
        ]
      

      Actual results:

      -- dictionary:
        [
          "b",
          ""
        ]
      -- indices:
        [
          0,
          0,
          1
        ]
      

      I don't know a workaround. Converting to pylist and back is too slow. Is there a way to copy the slice to a new offset-0 StringArray that I could then dictionary-encode? Otherwise, I'm considering building buffers by hand....

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              apitrou Antoine Pitrou
              adamhooper Adam Hooper
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                Resolved:

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