Question

I have an array containing an even number of integers. The array represents a pairing of an identifier and a count. The tuples have already been sorted by the identifier. I would like to merge a few of these arrays together. I have thought of a few ways to do it but they are fairly complicated and I feel there might be an easy way to do this with python.

IE:

[<id>, <count>, <id>, <count>]

Input:

[14, 1, 16, 4, 153, 21]
[14, 2, 16, 3, 18, 9]

Output:

[14, 3, 16, 7, 18, 9, 153, 21]

Answer 1

It would be better to store these as dictionaries than as lists (not just for this purpose, but for other use cases, such as extracting the value of a single ID):

x1 = [14, 1, 16, 4, 153, 21]
x2 = [14, 2, 16, 3, 18, 9]

# turn into dictionaries (could write a function to convert)
d1 = dict([(x1[i], x1[i + 1]) for i in range(0, len(x1), 2)])
d2 = dict([(x2[i], x2[i + 1]) for i in range(0, len(x2), 2)])

print d1
# {16: 4, 153: 21, 14: 1}

After that, you could use any of the solutions in this question to add them together. For example (taken from the first answer):

import collections

def d_sum(a, b):
    d = collections.defaultdict(int, a)
    for k, v in b.items():
        d[k] += v
    return dict(d)

print d_sum(d1, d2)
# {16: 7, 153: 21, 18: 9, 14: 3}