In this article, we learned to generate all possible permutations of a list by using itertools.permutations() function and recursive method. It defaults to the length of the list and hence generates all possible permutations. The below example uses recursion to generate all permutations of a list. Example: Recursion method to generate all permutations of a list Perm.extend(list(itertools.permutations(list1, r=i))) Iterating over the elements of the list using for loop, the itertools.permutations() function finds all the possible lengths. extend() function is used to add items to the empty list one after the other. The below example takes an empty list to store all permutations of all possible length of a given list. Example: Generate Permutations of a list Perm = list(itertools.permutations(list1, r)) It generates the permutations of the given length. The below example passes the given list and length as an argument to itertools.permutations() function. Perm = list(itertools.permutations(list1))Įxample: Generate successive 'r' length permutations of a list The below example passes the given list as an argument to itertools.permutations() function. We will also discuss the recursive method to generate all possible permutations of a list. Python provides a standard library tool to generate permutations by importing itertools package to implement the permutations method in python. We all have heard and studied the permutation concept in mathematics, likewise, Python supports some built-in functions to generate permutations of a list. The list is ordered, changeable, and allows duplicate values. Lists can be defined using any variable name and then assigning different values to the list in a square bracket. The list uses comma-separated values within square brackets to store data. Data inside the list can be of any type say, integer, string or a float value, or even a list type. It is like a collection of arrays with different methodology. Python has a built-in data type called list. Let's first have a quick look over what is a list and what is permutation in Python. We will use some built-in functions and some custom codes as well. Interesting.In this article, we will learn how to generate all possible permutations of a list in Python. Right: movie plot (“Predestination”, 2014). Three images from an Internet search for “too complicated”. Let me emphasize that the “clever” approach would never be used in practice - it’s just way too complicated. I used the built-in NumPy argsort() function to get a permutation of (3, 2, 0, 1, 5, 6, 4) which when applied to the array will give an array that’s sorted in alphabetical order which makes it easy to tell if the demo code is working correctly or not. I coded a demo where I set an array = (“cow”, “dog”, “bat”, “ant”, “gnu”, “elk”, “fox”). There is a slightly different version of this algorithm that reduces the number iterations in the while-loop at the expense of having to track changes by modifying the perm parameter. The algorithm is quite subtle and the only way to really understand it (for me at least) is to walk through the code line by line and examine the values of i, j, and the source array. An old interview question asks how to apply a permutation to an array in place, without using a result array. Notice the code above creates a result array and then copies into that array. The best way to implement this as a function is very simple. In words, “the value in array cell 4 goes to result cell 0, the value in array cell 2 goes to result cell 1, the value in array cell 0 goes to result cell 2, the value in array cell 1 goes to result cell 3, the value in array cell 3 goes to result cell 4”. Suppose you have an array of (“C”, “E”, “A”, “B”, “D”) and the problem is to apply the permutation to the array. For example, one permutation of order 5 is (4, 2, 0, 1, 3). A permutation of order n is an arrangement of the numbers 0 through n-1.
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