# Python program to get all unique combinations of two Lists

The combination is a mathematical technique which calculates the number of possible arrangements in a collection of items or list. In combination order of selection doesn’t matter. The unique combination of two lists in Python can be formed by pairing each element of the first list with the elements of the second list.

Example:

```List_1 = ["a","b"]
List_2 = [1,2]
Unique_combination = [[('a',1),('b',2)],[('a',2),('b',1)]]
```

Method 1 : Using permutation() of itertools package and zip() function.

Approach :

• Import itertools package and initialize list_1 and list_2.
• Create an empty list of ‘unique_combinations’ to store the resulting combinations so obtained.
• Call itertools.permutations( ) which will return permutations of list_1 with length of list_2. Generally, the length of the shorter list is taken and if both lists are equal, use either.
• For loop is used and zip() function is called to pair each permutation and shorter list element into the combination.
• Then each combination is converted into a list and append to the combination list.

Below is the implementation.

## Python3

 `# python program to demonstrate ` `# unique combination of two lists ` `# using zip() and permutation of itertools ` ` `  `# import itertools package ` `import` `itertools ` `from` `itertools ``import` `permutations  ` ` `  `# initialize lists ` `list_1 ``=` `[``"a"``, ``"b"``, ``"c"``,``"d"``] ` `list_2 ``=` `[``1``,``4``,``9``] ` ` `  `# create empty list to store the ` `# combinations ` `unique_combinations ``=` `[] ` ` `  `# Getting all permutations of list_1  ` `# with length of list_2 ` `permut ``=` `itertools.permutations(list_1, ``len``(list_2)) ` ` `  `# zip() is called to pair each permutation ` `# and shorter list element into combination ` `for` `comb ``in` `permut: ` `    ``zipped ``=` `zip``(comb, list_2) ` `    ``unique_combinations.append(``list``(zipped)) ` ` `  `# printing unique_combination list  ` `print``(unique_combinations) `

Output :

[[(‘a’, 1), (‘b’, 4), (‘c’, 9)], [(‘a’, 1), (‘b’, 4), (‘d’, 9)], [(‘a’, 1), (‘c’, 4), (‘b’, 9)], [(‘a’, 1), (‘c’, 4), (‘d’, 9)], [(‘a’, 1), (‘d’, 4), (‘b’, 9)], [(‘a’, 1), (‘d’, 4), (‘c’, 9)], [(‘b’, 1), (‘a’, 4), (‘c’, 9)], [(‘b’, 1), (‘a’, 4), (‘d’, 9)], [(‘b’, 1), (‘c’, 4), (‘a’, 9)], [(‘b’, 1), (‘c’, 4), (‘d’, 9)], [(‘b’, 1), (‘d’, 4), (‘a’, 9)], [(‘b’, 1), (‘d’, 4), (‘c’, 9)], [(‘c’, 1), (‘a’, 4), (‘b’, 9)], [(‘c’, 1), (‘a’, 4), (‘d’, 9)], [(‘c’, 1), (‘b’, 4), (‘a’, 9)], [(‘c’, 1), (‘b’, 4), (‘d’, 9)], [(‘c’, 1), (‘d’, 4), (‘a’, 9)], [(‘c’, 1), (‘d’, 4), (‘b’, 9)], [(‘d’, 1), (‘a’, 4), (‘b’, 9)], [(‘d’, 1), (‘a’, 4), (‘c’, 9)], [(‘d’, 1), (‘b’, 4), (‘a’, 9)], [(‘d’, 1), (‘b’, 4), (‘c’, 9)], [(‘d’, 1), (‘c’, 4), (‘a’, 9)], [(‘d’, 1), (‘c’, 4), (‘b’, 9)]]

Method 2 : Using product() of itertools package and zip() function.

Approach :

• Import itertools package and initialize list_1 and list_2.
• Create an empty list of ‘unique_combinations’ to store the resulting combinations so obtained.
• product() is called to find all possible combinations of elements.
• And zip() is used to pair up all these combinations, converting each element into a list and append them to the desired combination list.

Below is the implementation.

## Python3

 `# python program to demonstrate ` `# unique combination of two lists ` `# using zip() and product() of itertools ` ` `  `# import itertools package ` `import` `itertools ` `from` `itertools ``import` `product  ` ` `  `# initilize lists ` `list_1 ``=` `[``"b"``,``"c"``,``"d"``] ` `list_2 ``=` `[``1``,``4``,``9``] ` ` `  `# create empty list to store the combinations ` `unique_combinations ``=` `[] ` ` `  `# Extract Combination Mapping in two lists  ` `# using zip() + product()  ` `unique_combinations ``=` `list``(``list``(``zip``(list_1, element)) ` `                           ``for` `element ``in` `product(list_2, repeat ``=` `len``(list_1))) ` ` `  `# printing unique_combination list  ` `print``(unique_combinations)`

Output :

[[(‘b’, 1), (‘c’, 1), (‘d’, 1)], [(‘b’, 1), (‘c’, 1), (‘d’, 4)], [(‘b’, 1), (‘c’, 1), (‘d’, 9)], [(‘b’, 1), (‘c’, 4), (‘d’, 1)], [(‘b’, 1), (‘c’, 4), (‘d’, 4)], [(‘b’, 1), (‘c’, 4), (‘d’, 9)], [(‘b’, 1), (‘c’, 9), (‘d’, 1)], [(‘b’, 1), (‘c’, 9), (‘d’, 4)], [(‘b’, 1), (‘c’, 9), (‘d’, 9)], [(‘b’, 4), (‘c’, 1), (‘d’, 1)], [(‘b’, 4), (‘c’, 1), (‘d’, 4)], [(‘b’, 4), (‘c’, 1), (‘d’, 9)], [(‘b’, 4), (‘c’, 4), (‘d’, 1)], [(‘b’, 4), (‘c’, 4), (‘d’, 4)], [(‘b’, 4), (‘c’, 4), (‘d’, 9)], [(‘b’, 4), (‘c’, 9), (‘d’, 1)], [(‘b’, 4), (‘c’, 9), (‘d’, 4)], [(‘b’, 4), (‘c’, 9), (‘d’, 9)], [(‘b’, 9), (‘c’, 1), (‘d’, 1)], [(‘b’, 9), (‘c’, 1), (‘d’, 4)], [(‘b’, 9), (‘c’, 1), (‘d’, 9)], [(‘b’, 9), (‘c’, 4), (‘d’, 1)], [(‘b’, 9), (‘c’, 4), (‘d’, 4)], [(‘b’, 9), (‘c’, 4), (‘d’, 9)], [(‘b’, 9), (‘c’, 9), (‘d’, 1)], [(‘b’, 9), (‘c’, 9), (‘d’, 4)], [(‘b’, 9), (‘c’, 9), (‘d’, 9)]]

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