Vectorized way to count occurrences of string in either of two columns

Question

I have a problem that is similar to this question, but just different enough that it can\'t be solved with the same solution...

I\'ve got two dataframes,

Answer 1

By using get_dummies

pd.get_dummies(df1, prefix='', prefix_sep='').sum(level=0,axis=1).gt(0).sum().loc[df2.ID]
Out[614]: 
jack        3
jill        5
jane        8
joe         9
ben         7
beatrice    6
dtype: int64

I think this should be fast ...

from itertools import chain
from collections import Counter

pd.Series(Counter(list(chain(*list(map(set,df1.values)))))).loc[df2.ID]