Missing item when performing a "for" loop

Question

I have a dictionary that has English words as keys and Finnish words as values. I'm trying to make a function to reverse this dictionary.

For example:

dictionary = {'move':['liikutta'], 'six':['kuusi'], 'fir':['kuusi']}

Expected output:

reverse = {'liikutta':['move'], 'kuusi':['six'], 'kuusi':['fir']}

The codes I'm using:

    def reverse_dictionary(dictionary):
    reverse = {}
    for key, value in dictionary.items():
         for i in range(len(value)):
             reverse.update({value[i]:[key]})
    return reverse

The 2nd item in the dictionary was skipped. I guess it was because the repeated 'kuusi', but I don't know how to solve it.

Output

{'liikutta':['move'], 'kuusi':['fir']}

Thanks all!

Dict cannot have duplicate keys, check [`link`](https://stackoverflow.com/a/10664876/4985099) — sushanth, Oct 02 '22 at 12:24
You can't solve it. Keys in dictionary must be unique. https://docs.python.org/3/tutorial/datastructures.html#dictionaries You probably need a different data type. What do you think about this output: `{'liikutta':['move'], 'kuusi':['fir', "six"]}` — JacekK, Oct 02 '22 at 12:25
Modified: Is there any way to group 'six' and 'fir' into 'kuusi'. Like this: `{'liikutta':['move'], 'kuusi':['six', 'fir']}` — Sang Nguyen, Oct 02 '22 at 12:30

score 0 · Answer 1 · answered Oct 02 '22 at 12:32

Every key in a dictionary has to be unique. What you can do, is update the list.

dictionary = {'move': ['liikutta'], 'six': ['kuusi'], 'fir': ['kuusi']}


def reverse_dictionary(dictionary):
    reverse = dict()
    for key, value in dictionary.items():
        l = reverse.get(value[0], [])  # get the list or an empty list
        l.append(key)  # append the key
        reverse.update({value[0]: l})  # update the dictionary
    return reverse

reverse_dictionary(dictionary)

output:

{'liikutta': ['move'], 'kuusi': ['six', 'fir']}

In one line:

reverse.update({value[0]: reverse.get(value[0], []) + [key]})

score 0 · Answer 2 · answered Oct 02 '22 at 12:33

If you use a list as a value - as it is in the original dictionary - then you can do it like this.

from collections import defaultdict


def reverse_dictionary(dictionary):
    reverse = defaultdict(list)
    for key, values in dictionary.items():
        for value in values:
            reverse[value].append(key)
    return reverse


dictionary = {'move': ['liikutta'], 'six': ['kuusi'], 'fir': ['kuusi']}
print(reverse_dictionary(dictionary))

The result is defaultdict(<class 'list'>, {'liikutta': ['move'], 'kuusi': ['six', 'fir']}).

A defaultdict behaves like a normal dictionary, but it calls a factory function to supply missing values. In this case it's a list.

Darth Vader · Answer 3 · 2022-10-02T12:39:07.203

0

The straight and simple answer is NO. You can't have duplicate keys in a dictionary in Python, the keys should be unique in, And if you attempt to do so,it will just overwrite the previous value of the key.But you can have multiple values associated to a key

edited Oct 02 '22 at 12:39

answered Oct 02 '22 at 12:38

Darth Vader

1
3

score 0 · Answer 4 · answered Oct 02 '22 at 12:39

You can try:

dictionary = {'move':['liikutta'], 'six':['kuusi'], 'fir':['kuusi']}
reverse = {}
for key, value in dictionary.items():
    for i in value:

        if i in reverse.keys():
            reverse[i].append(key)
        else:
            reverse[i]=[key]
print(reverse)

Result:

{'liikutta': ['move'], 'kuusi': ['six', 'fir']}

Jacek Błocki · Answer 5 · 2022-10-02T13:25:25.233

0

Try this:

def revd(d):
    r = {}
    for k,v in d.items():
        for i in v:
            # below is ternary expression, it updates r 
            r[i].append(k) if i in r else r.setdefault(i,[k])
    return r

Side remark: Instead of

for i in range(len(value)):

use

for i, v in enumerate(value))

edited Oct 02 '22 at 13:25

answered Oct 02 '22 at 13:16

Jacek Błocki

452
3
9

Missing item when performing a "for" loop

5 Answers5