# Buggy code
def tile(cls, op):
    tensor = op.outputs[0]

    v = op.input
    k = op.k
    idx = itertools.count(0)
    if v.ndim == 2:
        check_chunks_unknown_shape(op.inputs, TilesError)
        chunks = []
        nsplit = []

        fx = lambda x, y: x - y + k
        in_nsplits = v.nsplits
        cum_size = [np.cumsum(s) for s in in_nsplits]
        for c in v.chunks:
            i, j = c.index
            ld_pos = cum_size[0][i] - 1, cum_size[1][j] - in_nsplits[1][j]
            ru_pos = cum_size[0][i] - in_nsplits[0][i], cum_size[1][j] - 1

            ld_fx = fx(*ld_pos)
            ru_fx = fx(*ru_pos)

            if (ld_fx > 0 and ru_fx > 0) or (ld_fx < 0 and ru_fx < 0):
                continue

            lu_pos = ru_pos[0], ld_pos[1]
            chunk_k = fx(*lu_pos)

            chunk_shape = _get_diag_shape(c.shape, chunk_k)
            chunk_idx = (next(idx),)
            chunk_op = op.to_chunk_op(chunk_k)
            chunk = chunk_op.new_chunk(
                [c], shape=chunk_shape, index=chunk_idx, order=tensor.order
            )
            nsplit.append(chunk_shape[0])
            chunks.append(chunk)

        new_op = op.copy()
        return new_op.new_tensors(
            op.inputs,
            op.outputs[0].shape,
            order=tensor.order,
            chunks=chunks,
            nsplits=(tuple(nsplit),),
        )
    else:
        return super().tile(op)


# Traceback (AttributeError)
In [3]: import pandas as pd

In [4]: data = pd.DataFrame(np.arange(20).reshape((4, 5)) + 1, columns=['a', 'b', 'c', 'd', 'e'])

In [6]: df = md.DataFrame(data)

In [7]: df.groupby(['a','b']).size().execute()
Unexpected exception occurred in enter_build_mode.<locals>.inner.
Traceback (most recent call last):
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/utils.py", line 353, in _wrapped
return func(*args, **kwargs)
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/utils.py", line 493, in inner
return func(*args, **kwargs)
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/scheduler/graph.py", line 633, in prepare_graph
self._target_tileable_datas + fetch_tileables, tileable_graph)
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/utils.py", line 399, in _wrapped
return func(*args, **kwargs)
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/utils.py", line 493, in inner
return func(*args, **kwargs)
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/tiles.py", line 350, in build
tileables, tileable_graph=tileable_graph)
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/utils.py", line 399, in _wrapped
return func(*args, **kwargs)
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/utils.py", line 493, in inner
return func(*args, **kwargs)
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/tiles.py", line 263, in build
self._on_tile_failure(tileable_data.op, exc_info)
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/tiles.py", line 302, in inner
raise exc_info[1].with_traceback(exc_info[2]) from None
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/tiles.py", line 243, in build
tiled = self._tile(tileable_data, tileable_graph)
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/tiles.py", line 338, in _tile
return super()._tile(tileable_data, tileable_graph)
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/tiles.py", line 203, in _tile
tds = on_tile(tileable_data.op.outputs, tds)
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/scheduler/graph.py", line 615, in on_tile
return self.context.wraps(handler.dispatch)(first.op)
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/context.py", line 69, in h
return func(*args, **kwargs)
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/utils.py", line 399, in _wrapped
return func(*args, **kwargs)
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/tiles.py", line 119, in dispatch
tiled = op_cls.tile(op)
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/dataframe/groupby/aggregation.py", line 481, in tile
return cls._tile_with_tree(op)
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/dataframe/groupby/aggregation.py", line 412, in _tile_with_tree
index = out_df.index_value.to_pandas()
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/dataframe/core.py", line 283, in to_pandas
return self._index_value.to_pandas()
File "/Users/hekaisheng/Documents/mars_dev/mars/mars/dataframe/core.py", line 197, in to_pandas
sortorder=self._sortorder, names=self._names)
AttributeError: _sortorder

# Fixed code
def tile(cls, op):
    tensor = op.outputs[0]

    v = op.input
    k = op.k
    idx = itertools.count(0)
    if v.ndim == 2:
        check_chunks_unknown_shape(op.inputs, TilesError)
        chunks = []
        nsplit = []

        fx = lambda x, y: x - y + k
        in_nsplits = v.nsplits
        cum_size = [np.cumsum(s).tolist() for s in in_nsplits]
        for c in v.chunks:
            i, j = c.index
            ld_pos = cum_size[0][i] - 1, cum_size[1][j] - in_nsplits[1][j]
            ru_pos = cum_size[0][i] - in_nsplits[0][i], cum_size[1][j] - 1

            ld_fx = fx(*ld_pos)
            ru_fx = fx(*ru_pos)

            if (ld_fx > 0 and ru_fx > 0) or (ld_fx < 0 and ru_fx < 0):
                continue

            lu_pos = ru_pos[0], ld_pos[1]
            chunk_k = fx(*lu_pos)

            chunk_shape = _get_diag_shape(c.shape, chunk_k)
            chunk_idx = (next(idx),)
            chunk_op = op.to_chunk_op(chunk_k)
            chunk = chunk_op.new_chunk(
                [c], shape=chunk_shape, index=chunk_idx, order=tensor.order
            )
            nsplit.append(chunk_shape[0])
            chunks.append(chunk)

        new_op = op.copy()
        return new_op.new_tensors(
            op.inputs,
            op.outputs[0].shape,
            order=tensor.order,
            chunks=chunks,
            nsplits=(tuple(nsplit),),
        )
    else:
        return super().tile(op)