Combination of 2 dictionaries with a shared key

Question

I have two dictionaries and you need to combine the values ​​of similar keys in them. Here is an example:

dict1 = {'key1':[value11,value12,value13] , 'key2':[value21,value22,value23]} dict2 = {'key1':[value14,value15] , 'key2':[value24,value25]} 

I used:

 dict3 = {} for key in (dict1.viewkeys() | dict2.keys()): if key in dict1: dict3.setdefault(key, []).append(dict1[key]) if key in dict2: dict3.setdefault(key, []).append(dict2[key]) 

which gives me:

 dict3 = {'key1':[[value11,value12,value13],[value14,value15]] , 'key2':[[value21,value22,value23],[value24,value25]]} 

I want just:

Desired conclusion :

  dict3 = {'key1':[value11,value12,value13,value14,value15] , 'key2':[value21,value22,value23,value24,value25]} 

Answer 1

All you have to do is change the append to extend , which will then add the list items, rather than the list itself. See the list docs for more information on the difference between append and extend .

 dict1 = {'key1':['value11','value12','value13'] , 'key2':['value21','value22','value23']} dict2 = {'key1':['value14','value15'] , 'key2':['value24','value25']} dict3 = {} for key in set().union(dict1, dict2): if key in dict1: dict3.setdefault(key, []).extend(dict1[key]) if key in dict2: dict3.setdefault(key, []).extend(dict2[key]) print(dict3) # {'key2': ['value21', 'value22', 'value23', 'value24', 'value25'], 'key1': ['value11', 'value12', 'value13', 'value14', 'value15']} 

Alternatively, you can use collections.defaultdict with the default setting of list , as shown below.

 from collections import defaultdict dict3 = defaultdict(list) for key in set().union(dict1, dict2): for dic in [dict1, dict2]: if key in dic: dict3[key] += dic[key] 

Answer 2

You can make it a lot easier, but if you want to use your code, just change append to extend

 dict1 = {'key1':['value11','value12','value13'] , 'key2':['value21','value22','value23']} dict2 = {'key1':['value14','value15'] , 'key2':['value24','value25']} dict3 = {} for key in (dict1.viewkeys() | dict2.keys()): if key in dict1: dict3.setdefault(key, []).extend(dict1[key]) if key in dict2: dict3.setdefault(key, []).extend(dict2[key]) print dict3 

output:

 {'key2': ['value21', 'value22', 'value23', 'value24', 'value25'], 'key1': ['value11', 'value12', 'value13', 'value14', 'value15']} 

You can read this post about ov append difference for extension

Answer 3

Here is a general method by which you can pass as many arguments as you want as a parameter.

 >>> def mix_dict(*args): res = {} for d in args: if not isinstance(d, dict): continue for k, v in d.iteritems(): res.setdefault(k, []) if isinstance(v, list): res[k].extend(v) else: res[k].append(v) return res >>> dict1 = {'key1':['value11','value12','value13'] , 'key2':['value21','value22','value23']} >>> dict2 = {'key1':['value14','value15'] , 'key2':['value24','value25']} >>> dict3 = mix_dict(dict1, dict2) >>> print dict3 ... {'key1': ['value11', 'value12', 'value13', 'value14', 'value15'], 'key2': ['value21', 'value22', 'value23', 'value24', 'value25']} 

Answer 4

Here is another way to do it.

You can support combining N dicts lists into a single list of lists using this function:

 def mergeDoLs(*dicts): def flatten(LoL): return [e for l in LoL for e in l] rtr={k:[] for k in set(flatten(d.keys() for d in dicts))} for k, v in flatten(d.items() for d in dicts): rtr[k].extend(v) return rtr 

For use:

 >>> dict1 = {'key1':['value11','value12','value13'] , 'key2':['value21','value22','value23'], 'key3':[1]} >>> dict2 = {'key1':['value14','value15'] , 'key2':['value24','value25']} >>> dict3 = {'key3':[2]} >>> mergeDoLs(dict1, dict2, dict3) {'key3': [1, 2], 'key2': ['value21', 'value22', 'value23', 'value24', 'value25'], 'key1': ['value11', 'value12', 'value13', 'value14', 'value15']}