how to aggregate elements of a list of tuples if the tuples have the same first element?

Question

I have a list in which each value is a list of tuples. for example this is the value which I extract for a key :

     [(\'1998-01-20\',8) , (\'1998-01-22\',4) ,         


        

Answer 1

Just use defaultdict:

from collections import defaultdict


DATA = [
    ('1998-01-20', 8),
    ('1998-01-22', 4),
    ('1998-06-18', 8),
    ('1999-07-15', 7),
    ('1999-07-21', 1),
]


groups = defaultdict(int)
for date, value in DATA:
    groups[date[:7]] += value


from pprint import pprint
pprint(groups)