Group list of dictionaries by value [duplicate]

Question

I have a list of dictionaries. How can i group that list by valaues.

list = [{a:1},{b:2},{c:1},{d:3},{e:2}]

Now my result should be like below

1:a,c
2:b,e
3:d

I tried using groupby from itertools. But i couldn't get the required result. I am using python 2.7.

Could you help me achieve this?

Answer 1

If you want to use groupby, the list has to be sorted by the same key you want to group by.

>>> lst = [{'a':1}, {'b':2}, {'c':1}, {'d':3}, {'e':2}]

>>> keyfunc = lambda d: next(iter(d.values()))

>>> sorted(lst, key=keyfunc)
[{'a': 1}, {'c': 1}, {'b': 2}, {'e': 2}, {'d': 3}]

>>> {k: [x for d in g for x in d] 
...  for k, g in itertools.groupby(sorted(lst, key=keyfunc), key=keyfunc)}
{1: ['a', 'c'], 2: ['b', 'e'], 3: ['d']}

Answer 2

Here's a possible solution without using any library.

def get_dict(list):
    res = {}

    for elem in list:
        k, v = elem.keys(), elem.values()

        if v[0] in res:
            res[v[0]].append(k[0])
        else:
            res[v[0]] = [k[0]]

    return res

With a list like yours, this would output a dictionary with the following format:

{ 1:[a,c], 2:[b, e], 3:[c] }

This is considering you're always going to have the same format as input. If not, you could just adjust what is read and saved.