Ian Rose created ARROW-16838:
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Summary: Schema inference for pandas extension dtypes fails on
indexes
Key: ARROW-16838
URL: https://issues.apache.org/jira/browse/ARROW-16838
Project: Apache Arrow
Issue Type: Bug
Components: Python
Affects Versions: 8.0.0
Reporter: Ian Rose
Hi! pa.Schema.from_pandas called on a dataframe whose index is a pandas
extension dtype (e.g., string[python]) results in an error:
{code:python}
import pyarrow as pa
df = pd.DataFrame({"a": [1, 2]}, index=pd.Index(["A", "B"], dtype="string"))
pa.Schema.from_pandas(df)
{code}
produces
{code:python}
AttributeError Traceback (most recent call last)
/tmp/ipykernel_1827952/3691394220.py in <module>
1 import pyarrow as pa
2 df = pd.DataFrame({"a": [1, 2]}, index=pd.Index(["A", "B"],
dtype="string"))
----> 3 pa.Schema.from_pandas(df)
~/miniconda3/envs/dask/lib/python3.8/site-packages/pyarrow/types.pxi in
pyarrow.lib.Schema.from_pandas()
~/miniconda3/envs/dask/lib/python3.8/site-packages/pyarrow/pandas_compat.py in
dataframe_to_types(df, preserve_index, columns)
527 type_ = pa.array(c, from_pandas=True).type
528 elif _pandas_api.is_extension_array_dtype(values):
--> 529 type_ = pa.array(c.head(0), from_pandas=True).type
530 else:
531 values, type_ = get_datetimetz_type(values, c.dtype, None)
AttributeError: 'Index' object has no attribute 'head'
{code}
If I remove the `head` call, or convert the index to a series manually, things
work.
Reported downstream in https://github.com/dask/dask/issues/9186
Related issue from a couple of years ago:
https://issues.apache.org/jira/browse/ARROW-8159
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