Reset Cumulative sum base on condition Pandas

Question

I have a data frame like:

customer spend hurdle 
A         20    50      
A         31    50      
A         20    50      
B         50    100     
B                


        

Answer 1

One way would be the below code. But it's a really inefficient and inelegant one-liner.

df1.groupby('customer').apply(lambda x: (x['spend'].cumsum() *(x['spend'].cumsum() > x['hurdle']).astype(int).shift(-1)).fillna(x['spend']))