Python all pairs from list
Sometimes, while working with Python list, we can have a problem in which we need to extract all the possible pairs that can be performed from integers from list. This kind of problem can occur in many domains such as day-day programming and web development. Let’s discuss certain ways in which this task can be performed. Show
Method #1 : Using list comprehension +
Output : The original list : [1, 7, 4, 3] All possible pairs : [(1, 7), (1, 4), (1, 3), (7, 4), (7, 3), (4, 3)] Method #2 : Using
Output : The original list : [1, 7, 4, 3] All possible pairs : [(1, 7), (1, 4), (1, 3), (7, 4), (7, 3), (4, 3)] Given a list. The task is to write a Python program to get all pairwise combinations from the list. Finding all Pairs (No uniqueness)Example:
Method 1: Using simple loops We can access all combinations of the list using two loops to iterate over list indexes. If both the index counters are on the same index value, we skip it, else we print the element at index i followed by the element at index j in order. The time complexity of this method is O(n2) since we require two loops to iterate over lists. Python3
Output:
Method 2: Using itertools Python provides support of itertools standard library which is used to create iterators for efficient looping. The library provides support for various kinds of iterations, in groups, sorted order, etc. The permutations() functions of this library are used to get through all possible orderings of the list of elements, without any repetitions. The permutations() functions have the following syntax: itertools.permutations(lst,r) Where r depicts the r-length tuples, that is, 2 depicts a pair,3 depicts a triplet. The first argument is the specified list. The function returns the list of groups of elements returned after forming the permutations. The output contains n x (n-1) number of elements, where n is the size of the list since each element is subsequently is multiplied with all others. The time required to compute permutations is roughly exponential in the order of the size of the list. Python3
Output:
Note:
Python3
Output : (2, 2) (2, 2) (2, 2) (2, 2) (2, 2) (2, 2) Finding all Unique Pairs (Uniqueness)However, the permutations’ method doesn’t distinguish between (a, b) and (b, a) pairs and returns them both. The itertools library also supports a combinations() method that prints either of the (a, b) or (b, a) pairs and not both. The output number of elements is equivalent to (n-1)! where n is the length of the list. The time required to compute combinations is roughly polynomial. Example:
Python3
Output:
How do you find all pairs in Python?First, we take an empty list 'res' and start a loop and traverse each element of the given list of integers. In each iteration, pop the element, store it in 'num', find remaining difference for sum K, and check if the difference exists in the given list or not.
How do I get a list of two pairs in Python?How to get all unique combinations of two lists in Python. list1 = ["a", "b", "c"]. list2 = [1, 2]. all_combinations = []. list1_permutations = itertools. permutations(list1, len(list2)) ... . for each_permutation in list1_permutations:. zipped = zip(each_permutation, list2). all_combinations. ... . print(all_combinations). How do you create a pair from a list in Python?In this article, we are going to learn how to make pairs from two lists such that no similar elements make a pair.. Initialize the lists with elements.. Iterate over the lists and append the pair into a list if the corresponding elements from the lists are not same.. Print the result.. What is pair () in Python?Pairing functions take two integers and give you one integer in return. What makes a pairing function special is that it is invertable; You can reliably depair the same integer value back into it's two original values in the original order.
|