Florian Jetter created ARROW-2194:
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Summary: Pandas columns metadata incorrect for empty string columns
Key: ARROW-2194
URL: https://issues.apache.org/jira/browse/ARROW-2194
Project: Apache Arrow
Issue Type: Bug
Components: Python
Affects Versions: 0.8.0
Reporter: Florian Jetter
The {{pandas_type}} for {{bytes}} or {{unicode}} columns of an empty pandas
DataFrame is unexpectedly {{float64}}
{code}
import numpy as np
import pandas as pd
import pyarrow as pa
import json
empty_df = pd.DataFrame({'unicode': np.array([], dtype=np.unicode_), 'bytes':
np.array([], dtype=np.bytes_)})
empty_table = pa.Table.from_pandas(empty_df)
json.loads(empty_table.schema.metadata[b'pandas'])['columns']
# Same behavior for input dtype np.unicode_
[{u'field_name': u'bytes',
u'metadata': None,
u'name': u'bytes',
u'numpy_type': u'object',
u'pandas_type': u'float64'},
{u'field_name': u'unicode',
u'metadata': None,
u'name': u'unicode',
u'numpy_type': u'object',
u'pandas_type': u'float64'},
{u'field_name': u'__index_level_0__',
u'metadata': None,
u'name': None,
u'numpy_type': u'int64',
u'pandas_type': u'int64'}]{code}
Tested on Debian 8 with python2.7 and python 3.6.4
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