Zip two lists in dictionary but keep duplicates in key

Question

I have two lists:

alist = ['key1','key2','key3','key3','key4','key4','key5']

blist=  [30001,30002,30003,30003,30004,30004,30005]

I want to merge these lists and add them to a dictionary.

I try dict(zip(alist,blist)) but this gives:

{'key3': 30003, 'key2': 30002, 'key1': 30001, 'key5': 30005, 'key4': 30004}

The desired form of the dictionary is:

{'key1': 30001, 'key2': 30002, 'key3': 30003,'key3':30003, 'key4': 30004, 'key4': 30004, 'key5': 30005}

I want to keep the duplicates in the dictionary as well as not join the values in the same key (... key3': 30003,'key3':30003,... ).Is it possible?

Thanks in advance.

why would you want to keep the duplicates tho? They have an information density of 0 so to speak — Ma0, May 31 '17 at 09:07
Yes, a dictionary has to have unique, hashable keys, so you'll need to look at non-keyed collections such as lists or tuples. Sets, as you're probably aware, will also remove duplicates. There's another possible solution [here](https://stackoverflow.com/questions/10664856/make-dictionary-with-duplicate-keys-in-python) — DatHydroGuy, May 31 '17 at 09:09
Yes, use list or tuple as mentioned. Try this code: tuple(zip(alist, blist)) or list(zip(alist, blist)). — Sanchit, May 31 '17 at 09:14

Moinuddin Quadri · Accepted Answer · 2022-01-27T17:47:33.483

You can not do this as dict objects can only have unique keys. Instead, you should use the list of tuple:

>>> alist = ['key1','key2','key3','key3','key4','key4','key5']
>>> blist=  [30001,30002,30003,30003,30004,30004,30005]

>>> zip(alist, blist)
[('key1', 30001), ('key2', 30002), ('key3', 30003), ('key3', 30003), ('key4', 30004), ('key4', 30004), ('key5', 30005)]

If you want to access all the values based on the key, you may use collections.defaultdict as:

>>> from collections import defaultdict

>>> my_dict = defaultdict(list)
>>> for k, v in zip(alist, blist):
...     my_dict[k].append(v)
...
>>> my_dict
defaultdict(<type 'list'>, {'key3': [30003, 30003], 'key2': [30002], 'key1': [30001], 'key5': [30005], 'key4': [30004, 30004]})

You can access defaultdict similar to normal dict objects. For example:

>>> my_dict['key3']
[30003, 30003]

score 3 · Answer 2 · answered May 31 '17 at 09:06

3

A dictionary uses UNIQUE keys, so its imposible to have duplicates.

answered May 31 '17 at 09:06

Netwave

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score 2 · Answer 3 · answered May 31 '17 at 09:20

As dict must use unique keys only, and if you insert same key twice the last one will be stored - this might be something you can use:

from itertools import groupby

alist = ['key1','key2','key3','key3','key4','key4','key5']
alist = [i for i, j in groupby(alist)]

blist = [30001,30002,30003,30003,30004,30004,30005]
blist = [list(j) for i, j in groupby(blist)]

print dict(zip(alist, blist))
#{'key3': [30003, 30003], 'key2': [30002], 'key1': [30001], 'key5': [30005], 'key4': [30004, 30004]}

If you want to preserve the key order as well you can use OrderedDict:

from collections import OrderedDict
print OrderedDict(zip(alist, blist))

This solution does not group `blist` using the key in `alist`, it just groups `blist` by common values, which I don't think is what we're after. For example if we have `['a', 'a', 'b']` and `[1, 2, 3]` we want `{'a': [1, 2], 'b': [3]}`. This solution does not achieve this. — ru111, Sep 26 '22 at 17:13

UNagaswamy · Answer 4 · 2022-08-23T20:48:09.670

0

Great answer by @MoinuddinQuadri. I expanded it further to get the index as well:

my_dict = defaultdict(list)
for idx, tup in enumerate(zip(alist, blist)):
    my_dict[tup[0]].append((idx, tup[1])

edited Aug 23 '22 at 20:48

answered Aug 23 '22 at 16:09

UNagaswamy

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Zip two lists in dictionary but keep duplicates in key

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