Sum multiple values for same key in lists using python

Question

I have a list which looks like this:

(151258350, 2464)
(151258350, 56)
(151262958, 56)
(151258350, 56)
(151262958, 112)
(151262958, 112)
(151259627, 56)
(151262958, 112)
(151262958, 56)

And I want a result that looks like this:

151259627 56
151262958 448
151258350 2576

And here's my code:

for key, vals in d.items():
    tempList.append((key, reduce(add, vals))) 

here, d is the list with the key-value pair. tempList is the List in which the values will be appended after summing them by key. and add is a fuction:

def add(x, y): return x+y

If this question has already been asked, please point me there as I was unsuccessful in finding it myself.

Answer 1

Use a Counter:

>>> l = [(151258350, 2464),
(151258350, 56),
(151262958, 56),
(151258350, 56),
(151262958, 112),
(151262958, 112),
(151259627, 56),
(151262958, 112),
(151262958, 56)]
>>> c = Counter()
>>> for k, v in l:
        c[k] += v

>>> c
Counter({151258350: 2576, 151262958: 448, 151259627: 56})

Answer 2

num_list = [(151258350, 2464),
(151258350, 56),
(151262958, 56),
(151258350, 56),
(151262958, 112),
(151262958, 112),
(151259627, 56),
(151262958, 112),
(151262958,56)]
num_dict = {}
for t in num_list:
    if t[0] in num_dict:
        num_dict[t[0]] = num_dict[t[0]]+t[1]
    else:
        num_dict[t[0]] = t[1]

for key,value in num_dict.items():
    print "%d %d" %(key,value)