How to use groupeby().count on a dataframe containing lists of values

Question

I have this kind to dataset :

I want to count and plot the occurence of each anomalie type in the dataframe.

I tried to use this :

r_bt.res_enquete_poteaux.groupby(by='type_anomalie')['type_anomalie'].count()

But it does not work as the column type_anomalie contains some lists.

Does somebody have an idea ?

Thanks !