Python | Zipping two unequal length list in dictionary

Given two lists of possibly unequal lengths, the task is to zip two lists in a dictionary such that the list with shorter length will repeat itself. Since the dictionary in Python is an unordered collection of key:value pairs, the result will be printed on unordered fashion. 

Method #1: Using itertools()

Python3

# Python code to demonstrate
# return the sum of values of a dictionary
# with same keys in the list of dictionary

from itertools import cycle

# Initialising list of dictionary
ini_lis1 = ['a', 'b', 'c', 'd', 'e']
ini_lis2 = [1, 2, 3]

# zipping in cyclic if shorter length
result = dict(zip(ini_lis1, cycle(ini_lis2)))

# printing resultant dictionary
print("resultant dictionary : ", str(result))

Output:

resultant dictionary :  {'b': 2, 'd': 1, 'c': 3, 'e': 2, 'a': 1}

Method #2: Using dict comprehension

Python3

# Python code to demonstrate
# return the sum of values of dictionary
# with same keys in list of dictionary

from itertools import cycle

# Initialising list of dictionary
ini_lis1 = ['a', 'b', 'c', 'd', 'e']
ini_lis2 = [1, 2, 3]

# zipping in cyclic if shorter length
result = {v: ini_lis2[i % len(ini_lis2)]
          for i, v in enumerate(ini_lis1)}

# Printing dictionary
print("resultant dictionary : ", str(result))

Output:

resultant dictionary :  {'d': 1, 'c': 3, 'e': 2, 'b': 2, 'a': 1}

Method #3: Using deque()

Python3

# Python code to demonstrate
# return the sum of values of dictionary
# with same keys in list of dictionary

from collections import deque

# Initialising list of dictionary
ini_lis1 = ['a', 'b', 'c', 'd', 'e']
ini_lis2 = deque([1, 2, 3])

# zipping in cyclic if shorter length
result = {}
for letter in ini_lis1:
    number = ini_lis2.popleft()
    result[letter] = number
    ini_lis2.append(number)

print("resultant dictionary : ", str(result))

Output:

resultant dictionary :  {'c': 3, 'd': 1, 'b': 2, 'e': 2, 'a': 1}

Method 4: Using a for loop and a default dictionary. 

1. Import defaultdict from the collections module.
2. Create an empty defaultdict named ‘result_dict’ with int as the default value type.
3. Loop through the ‘ini_lis1’ and ‘ini_lis2’ simultaneously using the built-in zip() function.
4. For each iteration, add the value in ‘ini_lis2’ to the corresponding key in ‘result_dict’.
5. Return ‘result_dict’.

Python

from collections import deque

# Initializing list of dictionary
ini_lis1 = ['a', 'b', 'c', 'd', 'e']
ini_lis2 = deque([1, 2, 3])

# Zipping in cyclic if shorter length
result = {}

for letter in ini_lis1:
    number = ini_lis2.popleft()
    if letter in result:
        result[letter] += number
    else:
        result[letter] = number
    ini_lis2.append(number)

# Printing dictionary
print("Resultant dictionary:", str(result))

Output

('Resultant dictionary:', "{'a': 1, 'c': 3, 'b': 2, 'e': 2, 'd': 1}")

Time complexity: O(n), where n is the length of the longest list (in this case, n = 5).
Auxiliary space: O(n), where n is the number of unique keys in the dictionary. In the worst case, each key has a different value and therefore each key-value pair needs to be stored in the dictionary.

Method #5: Using defaultdict

1. A defaultdict is a subclass of the built-in dictionary class. It overrides one method, missing(), which takes a key argument and returns a default value if the key is not present in the dictionary. 
2. In this case, we can use a defaultdict to automatically create a new key-value pair with a default value of 0 when we encounter a new key. 
3. We can then simply add the values to the corresponding keys.

Python3

from collections import defaultdict

# Initializing list of dictionaries
ini_lis1 = ['a', 'b', 'c', 'd', 'e']
ini_lis2 = [1, 2, 3]

# Creating defaultdict
result = defaultdict(int)

# Adding values to corresponding keys
for i in range(len(ini_lis1)):
    result[ini_lis1[i]] += ini_lis2[i % len(ini_lis2)]

# Printing resultant dictionary
print("resultant dictionary: ", str(dict(result)))

Output

resultant dictionary:  {'a': 1, 'b': 2, 'c': 3, 'd': 1, 'e': 2}

Time Complexity: O(n), where n is the length of the list of keys (ini_lis1).
Auxiliary Space: O(n)

Method #6: Using zip() and dict()

Python3

# Initializing list of dictionaries
ini_lis1 = ['a', 'b', 'c', 'd', 'e']
ini_lis2 = [1, 2, 3]

# Creating dictionary using zip()
result = dict(zip(ini_lis1, ini_lis2 *
                  ((len(ini_lis1) + len(ini_lis2) - 1) // len(ini_lis2))))

# Printing resultant dictionary
print("resultant dictionary: ", str(result))

Output

resultant dictionary:  {'a': 1, 'b': 2, 'c': 3, 'd': 1, 'e': 2}

Time Complexity: O(n), where n is the length of the list of keys (ini_lis1).
Auxiliary Space: O(n)