Merging two lists into dictionary while keeping duplicate data in python

Question

Hi, I want to merge two lists into one dictionary. Suppose I have two lists such as below

list_one = [\'a\', \'a\', \'c\', \'d\']

list_two = [1,2,3,4]

Answer 1

As other answers have pointed out, dictionaries have unique keys, however, it is possible to create a structure to mimic the behavior you are looking for:

class NewDict:
   def __init__(self, *values):
       self.values = list(zip(*values))
   def __getitem__(self, key):
        return [b for a, b in sorted(self.values, key=lambda x:x[0]) if a == key]
   def __repr__(self):
       return "{}({})".format(self.__class__.__name__, "{"+', '.join("{}:{}".format(*i) for i in sorted(self.values, key=lambda x:x[0]))+"}")

list_one = ['a', 'a', 'c', 'd']
list_two = [1,2,3,4]
d = NewDict(list_one, list_two)
print(d['a'])
print(d)

Output:

[1, 2]
NewDict({a:1, a:2, c:3, d:4})

Answer 2

You have two options :

either you use tuple :

list_one = ['a', 'a', 'c', 'd']

list_two = [1,2,3,4]



print(list(map(lambda x,y:(x,y),list_one,list_two)))

output:

[('a', 1), ('a', 2), ('c', 3), ('d', 4)]

Second option is use this pattern:

dict_1={}

for key,value in zip(list_one,list_two):
    if key not in dict_1:
        dict_1[key]=[value]
    else:
        dict_1[key].append(value)

print(dict_1)

output:

{'a': [1, 2], 'd': [4], 'c': [3]}

Answer 3

A defining characteristic of dicts is that each key is unique. Thus, you can't have two 'a' keys. Otherwise, what would my_dict['a'] return?

Answer 4

Since keys in dictionaries are unique, getting {'a': 1, 'a': 2, 'c': 3, 'd': 4} is impossible here for regular python dictionaries, since the key 'a' can only occur once. You can however have a key mapped to multiple values stored in a list, such as {'a': [1, 2], 'c': [3], 'd': [4]}.

One option is to create a defaultdict to do this easily for you:

from collections import defaultdict

list_one = ['a', 'a', 'c', 'd']

list_two = [1, 2, 3, 4]

d = defaultdict(list)
for key, value in zip(list_one, list_two):
    d[key].append(value)

print(dict(d))

Which outputs:

{'a': [1, 2], 'c': [3], 'd': [4]}

Answer 5

Dictionary has unique keys. If you need the value of 'a' separately store the zipped data in a list or you can use list in values part of the dict and store the values as: {'a': [1,2],'c': [3], 'd': [4]}

Answer 6

From the documentation for dictionaries:

It is best to think of a dictionary as an unordered set of key: value pairs, with the requirement that the keys are unique (within one dictionary). A pair of braces creates an empty dictionary: {}. Placing a comma-separated list of key:value pairs within the braces adds initial key:value pairs to the dictionary; this is also the way dictionaries are written on output.