Sum list of list of tuples

Question

I found that summing a list of list of number is:

In [9]: l = [[3,7,2],[1,4,5],[9,8,7]]
In [10]: [sum(i) for i in zip(*l)]
Out[10]: [13, 19, 14]

However I have been struggling to find a way to sum a list of list of tuples to result in a list of tuples

In [9]: l = [[(1, 1), (1, 1), (1, 1)],[(2, 2), (2, 2), (2, 2)]]
In [10]: [(sum(i[0]), sum(i[1])) for i in zip(*l)] #Did not work

This is my desired output:

Out[10]: [(3, 3), (3, 3), (3, 3)]

Thanks!

score 2 · Accepted Answer · answered Oct 17 '18 at 23:47

You can use a tuple comprehension within a list comprehension:

L = [[(1, 1), (1, 1), (1, 1)], [(2, 2), (2, 2), (2, 2)]]

res = [tuple(sum(j) for j in zip(*i)) for i in zip(*L)]

[(3, 3), (3, 3), (3, 3)]

Or use map for a more functional alternative:

res = [tuple(map(sum, zip(*i))) for i in zip(*L)]

For larger lists, you may wish to consider a 3rd party library such as NumPy where, in NumPy terminology, you need only sum over a specified axis:

import numpy as np

A = np.array(L)

res = A.sum(axis=0)

array([[3, 3],
       [3, 3],
       [3, 3]])

score 1 · Answer 2 · answered Oct 17 '18 at 23:51

You could flatten the iterable recursively first

>>> import collections
>>> 
>>> def flatten(l):
...     for el in l:
...         if isinstance(el, collections.Iterable) and not isinstance(el, str):
...             for sub in flatten(el):
...                 yield sub
...         else:
...             yield el
... 
>>> sum(flatten(l))
18

See this link for more details on flatten.

Sum list of list of tuples

2 Answers2