In [1]: import xorbits.pandas as pd

In [2]: df = pd.DataFrame({'a': ['a', 'b', 'a', 'c'], 'b': [0.1, 0.2, 0.3, 0.4], 'c': ['aa', 'bb', 'cc', 'aa']})

In [3]: grouped = df.groupby('b')

In [4]: len(grouped)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[4], line 1
----> 1 len(grouped)

File ~/Workspace/xorbits/python/xorbits/core/data.py:267, in DataRef.__len__(self)
    263             raise TypeError(
    264                 f"object with shape {self.data._mars_entity.shape} has no len()"
    265             )
    266 else:
--> 267     raise TypeError(f"object of type '{self.data.data_type}' has no len()")

TypeError: object of type 'DataType.dataframe_groupby' has no len()