Is there an easy way to sum all similar values in a list using list comprehensions?
i.e. input:
[1, 2, 1, 3, 3]
expected output:
[6, 2, 2] (sorted)
I tried using zip, but it only works for max 2 similar values:
[x + y for (x, y) in zip(l[:-1], l[1:]) if x == y]
from itertools import groupby
a=[1, 2, 1,1,4,5,5,5,5, 3, 3]
print sorted([sum(g) for i,g in groupby(sorted(a))],reverse=True)
#output=[20, 6, 4, 3, 2]
explantion for the code
first sort the list using sorted(a)
perform groupby to make groupf of similar elements
sum()
You can use collections.Counter for this, this will take O(N) time.:
>>> from collections import Counter
>>> lst = [1, 2, 1, 3, 3]
>>> [k*v for k, v in Counter(lst).iteritems()]
[2, 2, 6]
Here Counter() returns the count of each unique item, and then we multiply those numbers with their count to get the sum.
