Merging and adding dictionary values in comprehension

Question

I have the following three dictionaries:

d1 = {'python':15, 'java':2,'c#':3}
d2 = {'go':30,'c#':4, 'java':10,}
d3 = {'python':2,'ruby':7}

I have used the following code to merge and sum all values of the same keys.

d={}
for mydict in d1,d2,d3:
    for key in mydict:
        d[key] = d.get(key,0) + mydict[key]
print(d)

But I am not able to change this code into a comprehension.

I have already done it using collection.Counter and Itertools.chain() method.

I'd argue that it doesn't. Your code reads fine as it is to me (though you could make it more general to handle more than 3 dicts) — roganjosh, Sep 12 '20 at 10:15
@Heap Overflow Not Counter +chain, one solution use Counter, one solution use DefaultDict and chain — John, Sep 12 '20 at 12:23

snatchysquid · Answer 1 · 2020-09-12T10:04:13.697

0

Try this:

d = {}
d = {key: di[key] + d.get(key, 0) for di in (d1, d2, d3) for key in di}

Output:

{'python': 2, 'java': 10, 'c#': 4, 'go': 30, 'ruby': 7}

What we do is iterate over each key in each dict and add the corresponding key, value pair.

edited Sep 12 '20 at 10:04

answered Sep 12 '20 at 10:01

snatchysquid

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I want the values to add up like python:17 – John Sep 12 '20 at 10:03
@John understand, will fix – snatchysquid Sep 12 '20 at 10:04

score 0 · Answer 2 · answered Sep 12 '20 at 10:16

0

One way using collections.Counter:

from collections import Counter

sum([Counter(d) for d in [d1, d2, d3]], Counter())

Output:

Counter({'python': 17, 'java': 12, 'c#': 7, 'go': 30, 'ruby': 7})

answered Sep 12 '20 at 10:16

Chris

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yes I have already tried it using Counter and Chain method. But couldn't convert it to comprehension – John Sep 12 '20 at 10:19

score 0 · Answer 3 · answered Sep 12 '20 at 10:57

I am aware that the solution is not based on comprehension but I think it is more clear and direct.

from typing import List
from collections import defaultdict

def merge_dicts(dicts: List[dict]):
    result = defaultdict(int)
    for d in dicts:
        for k,v in d.items():
            result[k] += v
    return result


d1 = {'python':15, 'java':2,'c#':3}
d2 = {'go':30,'c#':4, 'java':10,}
d3 = {'python':2,'ruby':7}

final_dict = merge_dicts([d1,d2,d3])
print(final_dict)

output

defaultdict(<class 'int'>, {'python': 17, 'java': 12, 'c#': 7, 'go': 30, 'ruby': 7})

Merging and adding dictionary values in comprehension

3 Answers3