Inverting a dictionary when some of the original values are identical

Question

Say I have a dictionary called word_counter_dictionary that counts how many words are in the document in the form {\'word\' : number}. For example,

Answer 1

What you can do is convert the value in a list of words with the same key:

word_counter_dictionary = {'first':1, 'second':2, 'third':3, 'fourth':2}

inverted_dictionary = {}
for key in word_counter_dictionary:
    new_key = word_counter_dictionary[key]
    if new_key in inverted_dictionary:
        inverted_dictionary[new_key].append(str(key))
    else:
        inverted_dictionary[new_key] = [str(key)]

print inverted_dictionary

>>> {1: ['first'], 2: ['second', 'fourth'], 3: ['third']}