How to Reverse a Dictionary That Has Repeated Values

How to reverse a dictionary that has repeated values

Using collections.defaultdict:

from collections import defaultdict

reversed_dict = defaultdict(list)
for key, value in mydict.items():
    reversed_dict[value].append(key)

How to reverse a dictionary with repeated values as a set

just create a new dictionary

newdict = {}
for key, val in d.items():
   if val not in newdict:
        newdict[val] = key
   else:
        newdict[val] = set((*newdict[val], key))

How to reverse a dictionary in python and create a list out of the duplicate keys value

The most straightforward solution would be:

from collections import defaultdict

res = defaultdict(list)
for key, val in sorted(dic.items()):
    res[val].append(key)

The same can be done with vanilla dictionary:

res = {}
for i, v in d_input.items():
    res[v] = [i] if v not in res.keys() else res[v] + [i]

A neat solution using pandas:

import pandas as pd

pd.Series(dic).reset_index().groupby(0).agg(list).to_dict()['index']

how to invert a dictionary with multiple same values?

You are losing values because the values of the original dict (which can have duplicates) becomes keys in this one. You could do something like

inverted = defaultdict(list)

for key, value in original_dict.items():
    inverted[value].append(key)

How to create a reverse dictionary that takes in account repeated values?

You have to iterate over the values in the list as well:

def reversed_dict(d):
    new_dict = {}
    for keys,values in d.items():
        for val in values:
            new_dict.setdefault(val, []).append(keys)
   return new_dict

Removing inverse duplicates in dictionary python

You can turn each entry to a tuple and use a set to get O(n) time.

d = {'a': ['b'],
 'c': ['d'],
 'x': ['y'],
 'y': ['x'],
 'i': ['j','k'],
 'j': ['i','k'],
 'k': ['i','j']}

seen = set()
to_remove = []
for key, val in d.items():
    entry = tuple(sorted(val.copy() + [key]))
    to_remove.append(key) if entry in seen else seen.add(entry)

for key in to_remove:
    del d[key]
print(d)

Output:

{'a': ['b'], 'c': ['d'], 'x': ['y'], 'i': ['j', 'k']}

Reverse / invert a dictionary mapping

Python 3+:

inv_map = {v: k for k, v in my_map.items()}

Python 2:

inv_map = {v: k for k, v in my_map.iteritems()}

How to remove duplicated keys in reverse order from dictionary (python)

You could do something along the following lines:

d = {('cat', 'tiger'): 18,
     ('tiger', 'cat'): 18,
     ('chines', 'gentleman'): 7,
     ('gentleman', 'chines'): 7}

result = {tuple(sorted(x)): y for x, y in d.items()}
# {('cat', 'tiger'): 18, ('chines', 'gentleman'): 7}

In this dict comprehension, the last encountered value for each set of "equal" keys wins. With your sample data, this shouldn't matter because those keys have equla values. Note that this also just sorts the tuples, regardless of the sorted version actually occuring in the original dict.

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