python dict remove duplicate values by key's value?

Question

A dict

dic = {
 1: 'a', 
 2: 'a', 
 3: 'b', 
 4: 'a', 
 5: 'c', 
 6: 'd', 
 7: 'd', 
 8: 'a', 
 9: 'a'}

I want to remove duplicate values just keep one K/V pair, Regarding the "key" selection of those duplicated values, it may be max or min or by random select one of those duplicated item's key.

I do not want to use a k/v swap since that can not control the key selection.

Take value "a" for example

 1: 'a', 
 2: 'a', 
 4: 'a', 
 8: 'a', 
 9: 'a'

the max key will be {9: 'a'} and the min will be {1: 'a'}, and the random will choise any one of it.

And, if the key is other kind of hashable value, for example, string, then how to do such a selection?

Can anyone share me an idea?

Thanks!

Answer 1

You could build a reverse dictionary where the values are lists of all the keys from your initial dictionary. Using this you could then do what you want, min, max, random, alternate min and max, or whatever.

from collections import defaultdict

d = defaultdict(list)
for k,v in dic.iteritems():
    d[v].append(k)

print d
# {'a': [1, 2, 4, 8, 9], 'c': [5], 'b': [3], 'd': [6, 7]}