Merge and sum of two dictionaries

Question

I have a dictionary below, and I want to add to another dictionary with not necessarily distinct elements and merge it's results. Is there any built-in function for this, or will I need to make my own?

{   '6d6e7bf221ae24e07ab90bba4452267b05db7824cd3fd1ea94b2c9a8': 6,   '7c4a462a6ed4a3070b6d78d97c90ac230330603d24a58cafa79caf42': 7,   '9c37bdc9f4750dd7ee2b558d6c06400c921f4d74aabd02ed5b4ddb38': 9,   'd3abb28d5776aef6b728920b5d7ff86fa3a71521a06538d2ad59375a': 15,   '2ca9e1f9cbcd76a5ce1772f9b59995fd32cbcffa8a3b01b5c9c8afc2': 11 } 

The number of elements in the dictionary is also unknown.

Where the merge considers two identical keys, the values of these keys should be summed instead of overwritten.

Answer 1

You didn't say how exactly you want to merge, so take your pick:

x = {'both1': 1, 'both2': 2, 'only_x': 100} y = {'both1': 10, 'both2': 20, 'only_y': 200}  print {k: x.get(k, 0) + y.get(k, 0) for k in set(x)} print {k: x.get(k, 0) + y.get(k, 0) for k in set(x) & set(y)} print {k: x.get(k, 0) + y.get(k, 0) for k in set(x) | set(y)} 

Results:

{'both2': 22, 'only_x': 100, 'both1': 11} {'both2': 22, 'both1': 11} {'only_y': 200, 'both2': 22, 'both1': 11, 'only_x': 100} 

Answer 2

You can perform +, -, &, and | (intersection and union) with collections.Counter().

We can do the following (Note: only positive count values will remain in the dictionary):

from collections import Counter  x = {'both1':1, 'both2':2, 'only_x': 100 } y = {'both1':10, 'both2': 20, 'only_y':200 }  z = dict(Counter(x)+Counter(y))  print(z) [out]: {'both2': 22, 'only_x': 100, 'both1': 11, 'only_y': 200} 

To address adding values where the result may be zero or negative, use Counter.update() for addition, and Counter.subtract() for subtraction:

x = {'both1':0, 'both2':2, 'only_x': 100 } y = {'both1':0, 'both2': -20, 'only_y':200 } xx = Counter(x) yy = Counter(y) xx.update(yy) dict(xx) [out]: {'both2': -18, 'only_x': 100, 'both1': 0, 'only_y': 200}