[ARROW-1132] [Python] Unable to write pandas DataFrame w/MultiIndex containing duplicate values to parquet

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 0.4.1
• Fix Version/s: 0.5.0
• Component/s: Python
• Environment: OSx, miniconda, using pyarrow build from conda-forge
• External issue URL: https://github.com/apache/arrow/issues/15424
• Assignee: Phillip Cloud
• Reporter: Ben Mabey
• Created: 20/Jun/17 20:36
• Updated: 11/Jan/23 07:12
• Resolved: 23/Jun/17 19:29

Description

Panda DataFrames that have `MultiIndex`es seem to always be converted to a `Table` just fine. However, when writing the `Table` to disk using `pyarrow.parquet`, I am unable to write DataFrames whose `MultiIndex` contains a level with duplicate values (which is nearly always the case for me). Here is an example in python with working cases and a failure case at bottom:

import pandas as pd
import pyarrow as pa
import pyarrow.parquet as pq

num_rows = 3
example = pd.DataFrame({'strs': ['foo', 'foo', 'bar'],
                        'nums_b': range(num_rows),
                        'nums_a': range(num_rows)})


def pq_write(df):
    table = pa.Table.from_pandas(df)
    pq.write_table(table, '/tmp/df.parquet')

# single index works
pq_write(example)
pq_write(example.set_index(['nums_b']))

# single index with duplicate values work
pq_write(example.set_index(['strs']))

# MultiIndex with all unique, relative to the level/column, values works
pq_write(example.set_index(['nums_b', 'nums_a']))

# MultiIndex with one level with duplicate values in one index FAILS
pq_write(example.set_index(['strs', 'nums_a']))

Traceback (most recent call last):
  File "test_arrow.py", line 26, in <module>
    pq_write(example.set_index(['strs', 'nums_a']))
  File "test_arrow.py", line 13, in pq_write
    pq.write_table(table, '/tmp/df.parquet')
  File "/Users/bmabey/anaconda/envs/test_pyarrow/lib/python3.5/site-packages/pyarrow/parquet.py", line 702, in write_table
    writer.write_table(table, row_group_size=row_group_size)
  File "pyarrow/_parquet.pyx", line 609, in pyarrow._parquet.ParquetWriter.write_table (/Users/travis/miniconda3/conda-bld/pyarrow_1497322770287/work/arrow-46315431aeda3b6968b3ac4c1087f6d41052b99d/python/build/temp.macosx-10.9-x86_64-3.5/_parquet.cxx:11025)
  File "pyarrow/error.pxi", line 60, in pyarrow.lib.check_status (/Users/travis/miniconda3/conda-bld/pyarrow_1497322770287/work/arrow-46315431aeda3b6968b3ac4c1087f6d41052b99d/python/build/temp.macosx-10.9-x86_64-3.5/lib.cxx:6899)
pyarrow.lib.ArrowIOError: IOError: Written rows: 2 != expected rows: 3in the current column chunk

Note that the written rows is equal to the number of unique values in the `strs` level. I have found this to always be the case when I've hit this error message.

I'm happy to write a patch for this assuming this is a bug and you can point me in the right direction.