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Uwe L. Korn commented on ARROW-2194: ------------------------------------ The behaviour for this is different on master. You now get {{empty}} instead of {{float64}}: {code:java} [{'field_name': 'bytes', 'metadata': None, 'name': 'bytes', 'numpy_type': 'object', 'pandas_type': 'empty'}, {'field_name': 'unicode', 'metadata': None, 'name': 'unicode', 'numpy_type': 'object', 'pandas_type': 'empty'}, {'field_name': '__index_level_0__', 'metadata': None, 'name': None, 'numpy_type': 'int64', 'pandas_type': 'int64'}]{code} > [Python] 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 > Priority: Minor > Fix For: 0.9.0 > > > 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 -- This message was sent by Atlassian JIRA (v7.6.3#76005)