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https://issues.apache.org/jira/browse/ARROW-5138?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17662160#comment-17662160
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Rok Mihevc commented on ARROW-5138:
-----------------------------------
This issue has been migrated to [issue
#21620|https://github.com/apache/arrow/issues/21620] on GitHub. Please see the
[migration documentation|https://github.com/apache/arrow/issues/14542] for
further details.
> [Python/C++] Row group retrieval doesn't restore index properly
> ---------------------------------------------------------------
>
> Key: ARROW-5138
> URL: https://issues.apache.org/jira/browse/ARROW-5138
> Project: Apache Arrow
> Issue Type: Bug
> Components: C++, Python
> Affects Versions: 0.13.0
> Reporter: Florian Jetter
> Assignee: Wes McKinney
> Priority: Minor
> Labels: parquet, pull-request-available
> Fix For: 0.14.0
>
> Time Spent: 40m
> Remaining Estimate: 0h
>
> When retrieving row groups the index is no longer properly restored to its
> initial value and is set to an range index starting at zero no matter what.
> version 0.12.1 restored and int64 index with the correct index values.
> {code:python}
> import pandas as pd
> import pyarrow as pa
> import pyarrow.parquet as pq
> print(pa.__version__)
> df = pd.DataFrame(
> {"a": [1, 2, 3, 4]}
> )
> print("total DF")
> print(df.index)
> table = pa.Table.from_pandas(df)
> buf = pa.BufferOutputStream()
> pq.write_table(table, buf, chunk_size=2)
> reader = pa.BufferReader(buf.getvalue().to_pybytes())
> parquet_file = pq.ParquetFile(reader)
> rg = parquet_file.read_row_group(1)
> df_restored = rg.to_pandas()
> print("Row group")
> print(df_restored.index)
> {code}
> Previous behavior
> {code:python}
> 0.12.1
> total DF
> RangeIndex(start=0, stop=4, step=1)
> Row group
> Int64Index([2, 3], dtype='int64')
> {code}
> Behavior now
> {code:python}
> 0.13.0
> total DF
> RangeIndex(start=0, stop=4, step=1)
> Row group
> RangeIndex(start=0, stop=2, step=1)
> {code}
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