ueshin opened a new pull request #28210: [SPARK-31441] Support duplicated column names for toPandas with arrow execution. URL: https://github.com/apache/spark/pull/28210 ### What changes were proposed in this pull request? This PR is adding support duplicated column names for `toPandas` with Arrow execution. ### Why are the changes needed? When we execute `toPandas()` with Arrow execution, it fails if the column names have duplicates. ```py >>> spark.sql("select 1 v, 1 v").toPandas() Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/path/to/lib/python3.7/site-packages/pyspark/sql/dataframe.py", line 2132, in toPandas pdf = table.to_pandas() File "pyarrow/array.pxi", line 441, in pyarrow.lib._PandasConvertible.to_pandas File "pyarrow/table.pxi", line 1367, in pyarrow.lib.Table._to_pandas File "/path/to/lib/python3.7/site-packages/pyarrow/pandas_compat.py", line 653, in table_to_blockmanager columns = _deserialize_column_index(table, all_columns, column_indexes) File "/path/to/lib/python3.7/site-packages/pyarrow/pandas_compat.py", line 704, in _deserialize_column_index columns = _flatten_single_level_multiindex(columns) File "/path/to/lib/python3.7/site-packages/pyarrow/pandas_compat.py", line 937, in _flatten_single_level_multiindex raise ValueError('Found non-unique column index') ValueError: Found non-unique column index ``` ### Does this PR introduce any user-facing change? <!-- If yes, please clarify the previous behavior and the change this PR proposes - provide the console output, description and/or an example to show the behavior difference if possible. If no, write 'No'. --> Yes, previously we will face an error above, but after this PR, we will see the result: ```py >>> spark.sql("select 1 v, 1 v").toPandas() v v 0 1 1 ``` ### How was this patch tested? Added and modified related tests.
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