CODEWITHSUNDEEP
pythonpython-3.x
E.Keeya
E.Keeya

Reputation: 21

Summing a certain index values in lists within a list grouped by the first index value from each list

I have a list of lists as follows,

data = [[1, 2],[1, 10], [1, 4], [2, 3], [2, 2], [8, 3], [3,2]]

I want to group the inside lists by their first position value and then sum the second position values wherever there is a match like in the snippet below,

result = [[1,16],[2,5],[3,2],[8,3]]

how do I achieve this in pure python please?

Upvotes: 0

Views: 200

Answers (2)

Nick
Nick

Reputation: 147146

You can use itertools.groupby to group on the first value in each sublist, and then sum the second value in each grouped list:

from itertools import groupby

data = [[1, 2],[1, 10], [1, 4], [2, 3], [2, 2], [8, 3], [3,2]]

groups = groupby(data, key=lambda v:v[0])
result = [[i, sum(v[1] for v in g)] for i, g in groups]
print(result)

Output:

[[1, 16], [2, 5], [8, 3], [3, 2]]

Upvotes: 1

Leo Arad
Leo Arad

Reputation: 4472

You can use defaultdict for that to collect all the inner list first item and all these lists second items to a list and sum all of them.

from collections import defaultdict

data = [[1, 2],[1, 10], [1, 4], [2, 3], [2, 2], [8, 3], [3,2]]
res_dist = defaultdict(list)
for i in data:
    res_dist[i[0]].append(i[1])
print(sorted([[k, sum(v)] for k, v in res_dist.items()], key=lambda x: x[0]))

Output

[[1, 16], [2, 5], [3, 2], [8, 3]]

Upvotes: 0

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