Python summing values in list if it exists in another list

Question

I have a list and a set:

a_list = [[\'1\', 2], [\'2\', 1], [\'1\', 1]]

b_list = {\'1\', \'2\'}

I\'m looking to correspond the items in b_list

Answer 1

In [1]: a_list = [['1', 2], ['2', 1], ['1', 1]]
   ...:
   ...: b_list = {'1', '2'}

In [2]: out = [[i, sum(j[1] for j in a_list if j[0] == i)] for i in b_list]

In [3]: out
Out[3]: [['1', 3], ['2', 1]]

You can use sum of list or you can directly call sum. Here is a time performance of both approach:

In [6]: %timeit [[i, sum(j[1] for j in a_list if j[0] == i)] for i in b_list]
1.31 µs ± 2.52 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)

In [7]: %timeit [[i, sum([j[1] for j in a_list if j[0] == i])] for i in b_list]
1.2 µs ± 1.67 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)