Exception when grouping on a modified category #24740
Description
Code Sample, a copy-pastable example if possible
import pandas as pd ds = pd.DataFrame({"a": [1, 2, 3], "b": ["a", "b", "c"]}) ds["b"] = ds["b"].astype("category") ds['b'].cat.remove_categories(['a'], inplace=True) # works ds.groupby("b").groups # gives ValueError: Categorial categories cannot be null ds.groupby("b", observed=True).groupsProblem description
I wonder if that exception should be raised there?
Using 0.24 RC1
Thanks to all working on pandas!