将字典列表中的唯一值与Python中的相同键串联在一起

Question

I am working with a list of dictionaries and am trying to combine them into one with the following conditions:

1. The dictionaries in the list all have the same keys, and the new dictionary will as well
2. If the values for a given key across all dictionaries is the same, then that value will appear once in the value for the new dictionary
3. If the values for a given key across as dictionaries are unique, then the value for that key in the new dictionary will be a comma seperated string of all the values

So really what I am trying to do is create a set for a given key across multiple dictionaries, and create a comma seperated string of that set for the value in a new dictionary. To help visualize, given:

data = [ {"key1": "value1", "key2": "value2", "key3": "value3"},  
         {"key1": "value4", "key2": "value5", "key3": "value3"}, 
         {"key1": "value1", "key2": "value8", "key3": "value3"} ]

I want to make a new dictionary out of data that would like as follows:

myDict = {"key1": "value1, value4", "key2": "value2, value5, value8", "key3": "value3"}

Any ideas on how to accomplish this?

Answer 1

collections.defaultdict is your friend.

from collections import defaultdict
temp_dict = defaultdict(set)
for item in data:
   for key, value in item.items():
       temp_dict[key].add(value)

That gives you a dict in the form {"key1": ["value1", "value4"]} - if you want actual comma-separated strings for the values then you can join them:

my_dict = {}
for key, value in temp_dict.items():
    my_dict[key] = ", ".join(value)

Answer 2

I presumed two things here - that order of the values was not important to you, and that you did not mean to have two of the same keys in each dictionary (which I've replaced with "key3" ):

>>> data = [ {"key1": "value1", "key2": "value2", "key3": "value3"},
...          {"key1": "value4", "key2": "value5", "key3": "value3"},
...          {"key1": "value1", "key2": "value8", "key3": "value3"} ]
>>>
>>> keylist = data[0].keys()
>>> mydata = dict((k,', '.join(set(map(lambda d: d[k], data)))) for k in keylist)
>>> mydata
{'key3': 'value3', 'key2': 'value5, value2, value8', 'key1': 'value4, value1'}

Answer 3

In [3]: from itertools import chain
In [12]: dict([ (key, ",".join(set([elem[key] for elem in data]))) for key in set(list(chain(*[d.keys() for d in data])))])
Out[12]: {'key1': 'value4,value1', 'key2': 'value5,value2,value8', 'key3': 'value3'}