[jira] [Created] (ARROW-3065) concat_tables() failing from bad Pandas Metadata

["David Lee (JIRA)" <ji...@apache.org>]

David Lee created ARROW-3065:
--------------------------------

             Summary: concat_tables() failing from bad Pandas Metadata
                 Key: ARROW-3065
                 URL: https://issues.apache.org/jira/browse/ARROW-3065
             Project: Apache Arrow
          Issue Type: Bug
          Components: Python
    Affects Versions: 0.10.0
            Reporter: David Lee
             Fix For: 0.9.0


Looks like the major bug from https://issues.apache.org/jira/browse/ARROW-1941 is back...

After I downgraded from 0.10.0 to 0.9.0, the error disappeared..

{code:python}
new_arrow_table = pa.concat_tables(my_arrow_tables)

 File "pyarrow/table.pxi", line 1562, in pyarrow.lib.concat_tables
  File "pyarrow/error.pxi", line 81, in pyarrow.lib.check_status
pyarrow.lib.ArrowInvalid: Schema at index 2 was different:
{code}

In order to debug this I saved the first 4 arrow tables to 4 parquet files and inspected the parquet files. The parquet schema is identical, but the Pandas Metadata is different.

{code:python}
for i in range(5):
     pq.write_table(my_arrow_tables[i], "test" + str(i) + ".parquet")
{code}

It looks like a column which contains empty strings is getting typed as float64.

{code:python}
>>> test1.schema
HoldingDetail_Id: string
metadata
--------
{b'pandas': b'{"index_columns": [], "column_indexes": [], "columns": [
{"name": "HoldingDetail_Id", "field_name": "HoldingDetail_Id", "pandas_type": "unicode", "numpy_type": "object", "metadata": null},

>>> test1[0]
<Column name='HoldingDetail_Id' type=DataType(string)>
[
  [
    "Z4",
    "SF",
    "J7",
    "W6",
    "L7",
    "Q9",
    "NE",
    "F7",


>>> test2.schema
HoldingDetail_Id: string
metadata
--------
{b'pandas': b'{"index_columns": [], "column_indexes": [], "columns": [
{"name": "HoldingDetail_Id", "field_name": "HoldingDetail_Id", "pandas_type": "unicode", "numpy_type": "float64", "metadata": null},

>>> test2[0]
<Column name='HoldingDetail_Id' type=DataType(string)>
[
  [
    "",
    "",
    "",
    "",
    "",
    "",
    "",
    "",
{code}




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