[jira] [Created] (ARROW-6872) [C++][Python] Empty table with dictionary-columns raises ArrowNotImplementedError

["Marco Neumann (Jira)" <ji...@apache.org>]

Marco Neumann created ARROW-6872:
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             Summary: [C++][Python] Empty table with dictionary-columns raises ArrowNotImplementedError
                 Key: ARROW-6872
                 URL: https://issues.apache.org/jira/browse/ARROW-6872
             Project: Apache Arrow
          Issue Type: Bug
          Components: C++, Python
    Affects Versions: 0.15.0
            Reporter: Marco Neumann


h2. Abstract
As a pyarrow user, I would expect that I can create an empty table out of every schema that I created via pandas. This does not work for dictionary types (e.g. {{"category"}} dtypes).

h2. Test Case
This code:

{code:python}
import pandas as pd
import pyarrow as pa

df = pd.DataFrame({"x": pd.Series(["x", "y"], dtype="category")})
table = pa.Table.from_pandas(df)
schema = table.schema
table_empty = schema.empty_table()  # boom
{code}

produces this exception:

{noformat}
Traceback (most recent call last):
  File "arrow_bug.py", line 8, in <module>
    table_empty = schema.empty_table()
  File "pyarrow/types.pxi", line 860, in __iter__
  File "pyarrow/array.pxi", line 211, in pyarrow.lib.array
  File "pyarrow/array.pxi", line 36, in pyarrow.lib._sequence_to_array
  File "pyarrow/error.pxi", line 86, in pyarrow.lib.check_status
pyarrow.lib.ArrowNotImplementedError: Sequence converter for type dictionary<values=string, indices=int8, ordered=0> not implemented
{noformat}



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