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.

Asked By: e7lT2P

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Source

Answer 1

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]

Answered By: Moinuddin Quadri

Answer 2

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

Answered By: Netwave

Answer 3

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))

Answered By: zipa

Answer 4

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])

Answered By: UNagaswamy

Zip two lists in dictionary but keep duplicates in key

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