python - Combining two dictionaries into one with the same keys?

Question

I've looked through a few of the questions here and none of them seem to be exactly my problem. Say I have 2 dictionaries, and they are dict1

{'A': 25 , 'B': 41, 'C': 32}

and dict 2

{'A':21, 'B': 12, 'C':62}

I'm writing a program where I need to combine these to one dictionary finaldict

{'A': [25 , 21], 'B': [41, 12], 'C': [32, 62]}

Any help is much appreciated, I've been working on this and getting nowhere for a while now

Answer 1

This is a generic version. This can be used to create a dictionary with values as a list, even if the key is present in only one of them.

dic1 = {'A': 25, 'B': 41, 'C': 32}
dic2 = {'A': 21, 'B': 12, 'C': 62}
result = {}
for key in (dic1.keys() | dic2.keys()):
    if key in dic1: result.setdefault(key, []).append(dic1[key])
    if key in dic2: result.setdefault(key, []).append(dic2[key])

print(result)

Output

{'A': [25, 21], 'C': [32, 62], 'B': [41, 12]}

If you are using Python 2, for loop has to be changed like this:

for key in (dic1.viewkeys() | dic2.keys()):

Answer 2

As you know that your two dictionaries will always have the same keys, you could use:

finaldict = {key:(dict1[key], dict2[key]) for key in dict1}

to combine them, where each value would be a tuple of the values from the source dictionaries.

Answer 3

This is one way, using defaultdict:

# the setup
>>> from collections import defaultdict
>>> dict1 = {'A': 25, 'B': 41, 'C': 32}
>>> dict2 = {'A': 21, 'B': 12, 'C': 62}

# the preperation
>>> dicts = [dict1, dict2]
>>> final = defaultdict(list)

# the logic
>>> for k, v in ((k, v) for d in dicts for k, v in d.iteritems()):
    final[k].append(v)

# the result
>>> final 
defaultdict(<type 'list'>, {'A': [25, 21], 'C': [32, 62], 'B': [41, 12]})

Answer 4

def combineDict(dict1, dict2):
    res = collections.defaultdict(list)
    for key, value in (dict1.items() | dict2.items()):
        res[key].append(value)
    return res

print(combineDict(dict1, dict2))

Answer 5

This is another way to do it, and will work regardless if the keys are present in only one or in both dictionaries.

def merge_dicts(dict_a, dict_b):
    merged_dict = {key: [value] for key, value in dict_a.iteritems()}
    for key, value in dict_a.iteritems():
        try:
            merged_dict[key].append(value)
        except KeyError:
            meeged_dict[key] = [value]
    return ret_dict

Answer 6

I just needed to combine an unknown number dictionaries and after seeing answers to this question came up with more universal solutions:

1) dictionaries of values:

dic1 = {'A': 1, 'B': 1, 'C': 1}
dic2 = {'A': 2, 'B': 2, 'C': 2}
dic3 = {'D': 3, 'E': 3, 'F': 3}

def combineDictVal(*args):
    result = {}
    for dic in args:
        for key in (result.viewkeys() | dic.keys()):
            if key in dic:
                result.setdefault(key, []).append(dic[key])
    return result

print combineDictVal(dic1, dic2, dic3)

Result: {'A': [1, 2], 'C': [1, 2], 'B': [1, 2], 'E': [3], 'D': [3], 'F': [3]}

2) dictionaries of lists (difference is in append/extend*):

dic1 = {'A': [1, 2], 'B': [1, 2], 'C': [1, 2]}
dic2 = {'A': [3, 4], 'B': [3, 4], 'C': [3, 4]}
dic3 = {'D': [5, 6], 'E': [5, 6], 'F': [5, 6]}

def combineDictList(*args):
    result = {}
    for dic in args:
        for key in (result.viewkeys() | dic.keys()):
            if key in dic:
                result.setdefault(key, []).extend(dic[key])
    return result

print combineDictList(dic1, dic2, dic3)

Result: {'A': [1, 2, 3, 4], 'C': [1, 2, 3, 4], 'B': [1, 2, 3, 4], 'E': [5, 6], 'D': [5, 6], 'F': [5, 6]}

3) Universal for int / lists:

dic1 = {'A': 1, 'B': 1, 'C': [1, 1]}
dic2 = {'A': 2, 'B': [2, 2], 'C': 2}
dic3 = {'D': 3, 'E': 3, 'F': [3, 3]}

def combineDict(*args):
    result = {}
    for dic in args:
        for key in (result.viewkeys() | dic.keys()):
            if key in dic:
                if type(dic[key]) is list:
                    result.setdefault(key, []).extend(dic[key])
                else:
                    result.setdefault(key, []).append(dic[key])
    return result

print combineDict(dic1, dic2, dic3)

Result:

{'A': [1, 2], 'C': [1, 1, 2], 'B': [1, 2, 2], 'E': [3], 'D': [3], 'F': [3, 3]}

These solutions are not the fastest possible, however they are clear and work just fine. Hope it will help someone.

Answer 7

Use pydash

from pydash import merge_with
cbk = lambda obj_val, src_val: obj_val + src_val
obj1 = {'a': [1], 'b': [2]}
obj2 = {'a': [3], 'b': [4]}
res = merge_with(obj1, obj2, cbk)
print(res)

Result:

{'a': [1, 3], 'b': [2, 4]}

you can also use dictlib

import dictlib
obj1 = {'a': [1], 'b': [2]}
obj2 = {'a': [3], 'b': [4],"c":[3]}
c = dictlib.union_setadd(obj1, obj2)
print(c)    
{'a': [1, 3], 'b': [2, 4], 'c': [3]}