Brent Kerby created ARROW-2515: ---------------------------------- Summary: Errors with DictionaryArray inside of ListArray or other DictionaryArray Key: ARROW-2515 URL: https://issues.apache.org/jira/browse/ARROW-2515 Project: Apache Arrow Issue Type: Bug Components: Python Affects Versions: 0.9.0 Reporter: Brent Kerby
An exception ("KeyError: 26") is raised when .as_py() is called on elements of a ListArray over a DictionaryArray, or of a DictionaryArray with values in a DictionaryArray. Here are a couple tests that currently fail: {code:java} import pyarrow as pa def test_dictionary_array_1(): dict_arr = pa.DictionaryArray.from_arrays([0, 1, 0], ['a', 'b']) list_arr = pa.ListArray.from_arrays([0, 2, 3], dict_arr) assert list_arr.to_pylist() == [['a', 'b'], ['a']] def test_dictionary_array_2(): dict_arr = pa.DictionaryArray.from_arrays([0, 1, 0], ['a', 'b']) dict_arr2 = pa.DictionaryArray.from_arrays([0, 1, 2, 1, 0], dict_arr) assert dict_arr2.to_pylist() == ['a', 'b', 'a', 'b', 'a'] {code} It appears that the problem is caused by the fact that the function box_scalar in scalar.pxi does not handle the case of dictionary array, as we currently have no DictionaryValue type. DictionaryArray.__getitem__ currently works around the lack of DictionaryValue type by dereferencing the index and constructs a scalar based on the value in the underlying dictionary. In other words, if we have a dictionary with int8 indices and string values, then the result of __getitem__ will be a StringValue (rather than a DictionaryValue). This works in simple cases but not in the more complex scenarios illustrated above. I have a patch ready, which would add a DictionaryValue type similar to other scalar types, resolving these bugs and removing the need for a special-cased implementation of DictionaryArray.__getitem__. This DictionaryValue would contain a couple accessor properties, "indices_value" and "dictionary_value" to allow access to both the index in the dictionary as well as the looked-up value. Then DictionaryValue.as_py() would simply call .as_py() on the underlying dictionary_value. -- This message was sent by Atlassian JIRA (v7.6.3#76005)