load_dataset doesn't support list column
Author: arthasking123
State: open

### Describe the bug

dataset = load_dataset("Doraemon-AI/text-to-neo4j-cypher-chinese")

got exception:
Generating train split: 1834 examples [00:00, 5227.98 examples/s]
Traceback (most recent call last):
  File "/usr/local/lib/python3.11/dist-packages/datasets/builder.py", line 2011, in _prepare_split_single
    writer.write_table(table)
  File "/usr/local/lib/python3.11/dist-packages/datasets/arrow_writer.py", line 585, in write_table
    pa_table = table_cast(pa_table, self._schema)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/datasets/table.py", line 2295, in table_cast
    return cast_table_to_schema(table, schema)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/datasets/table.py", line 2254, in cast_table_to_schema
    arrays = [cast_array_to_feature(table[name], feature) for name, feature in features.items()]
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/datasets/table.py", line 2254, in <listcomp>
    arrays = [cast_array_to_feature(table[name], feature) for name, feature in features.items()]
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/datasets/table.py", line 1802, in wrapper
    return pa.chunked_array([func(chunk, *args, **kwargs) for chunk in array.chunks])
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/datasets/table.py", line 1802, in <listcomp>
    return pa.chunked_array([func(chunk, *args, **kwargs) for chunk in array.chunks])
                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/datasets/table.py", line 2018, in cast_array_to_feature
    casted_array_values = _c(array.values, feature[0])
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/datasets/table.py", line 1804, in wrapper
    return func(array, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/datasets/table.py", line 2115, in cast_array_to_feature
    raise TypeError(f"Couldn't cast array of type\n{array.type}\nto\n{feature}")
TypeError: Couldn't cast array of type
struct<m.name: string, x.name: string, p.name: string, n.name: string, h.name: string, name: string, c: int64, collect(r.name): list<item: string>, q.name: string, rel.name: string, count(p): int64, 1: int64, p.location: string, max(n.name): null, mn.name: string, p.time: int64, min(q.name): string>
to
{'q.name': Value(dtype='string', id=None), 'mn.name': Value(dtype='string', id=None), 'x.name': Value(dtype='string', id=None), 'p.name': Value(dtype='string', id=None), 'n.name': Value(dtype='string', id=None), 'name': Value(dtype='string', id=None), 'm.name': Value(dtype='string', id=None), 'h.name': Value(dtype='string', id=None), 'count(p)': Value(dtype='int64', id=None), 'rel.name': Value(dtype='string', id=None), 'c': Value(dtype='int64', id=None), 'collect(r.name)': Sequence(feature=Value(dtype='string', id=None), length=-1, id=None), '1': Value(dtype='int64', id=None), 'p.location': Value(dtype='string', id=None), 'substring(h.name,0,5)': Value(dtype='string', id=None), 'p.time': Value(dtype='int64', id=None)}

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/ubuntu/llm/train-2.py", line 150, in <module>
    dataset = load_dataset("Doraemon-AI/text-to-neo4j-cypher-chinese")
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dist-packages/datasets/load.py", line 2609, in load_dataset
    builder_instance.download_and_prepare(
  File "/usr/local/lib/python3.11/dist-packages/datasets/builder.py", line 1027, in download_and_prepare
    self._download_and_prepare(
  File "/usr/local/lib/python3.11/dist-packages/datasets/builder.py", line 1122, in _download_and_prepare
    self._prepare_split(split_generator, **prepare_split_kwargs)
  File "/usr/local/lib/python3.11/dist-packages/datasets/builder.py", line 1882, in _prepare_split
    for job_id, done, content in self._prepare_split_single(
  File "/usr/local/lib/python3.11/dist-packages/datasets/builder.py", line 2038, in _prepare_split_single
    raise DatasetGenerationError("An error occurred while generating the dataset") from e
datasets.exceptions.DatasetGenerationError: An error occurred while generating the dataset

### Steps to reproduce the bug

dataset = load_dataset("Doraemon-AI/text-to-neo4j-cypher-chinese")


### Expected behavior

no exception

### Environment info

python 3.11
datasets 2.19.0

Comments: I encountered this same issue when loading a customized dataset for ORPO training, in which there were three columns and two of them were lists. 
I debugged and found that it might be caused by the type-infer mechanism and because in some chunks one of the columns is always an empty list ([]), it was regarded as ```list<item: null>```, however in some other chunk it was ```list<item: string>```. This triggered a TypeError running the function ```table_cast()```.

I temporarily fixed this by re-dumping the file into a regular JSON format instead of lines of JSON dict. I didn't dig deeper for the lack of knowledge and programming ability but I do hope some developer of this repo will find and fix it.

My data were like following format:
{"messages": [{"content": "【角色与核心任务】  \n你是一个对话系统中xxxx，不用给出分类解释。", "role": "user"}, {"content": "[\"图文对话\"]", "role": "assistant"}], "images": ["xxx"]}
or  
{"messages": [{"content": "【角色与核心任务】  \n你是一个对话系统中xxxx，不用给出分类解释。", "role": "user"}, {"content": "[\"文文对话\"]", "role": "assistant"}], "images": []}

 I guess that continuous {...., "images":[]} would make this trouble. So, when I shuffle my data, the problem is solved!

It’s puzzling how the bug vanished overnight.