def to_sparse(self, fill_value=None, kind='block'):
"""
Convert to SparsePanel
Parameters
----------
fill_value : float, default NaN
kind : {'block', 'integer'}
Returns
-------
y : SparseDataFrame
"""
from pandas.core.sparse import SparsePanel
frames = dict(self.iterkv())
return SparsePanel(frames, items=self.items,
major_axis=self.major_axis,
minor_axis=self.minor_axis,
default_kind=kind,
default_fill_value=fill_value)
