Combination
This method takes a list and an input r as an input and return an object list of tuples which contain all possible combination of length r in a list form.
Python3
# A Python program to print all # combinations of given lengthfrom itertools import combinations# Get all combinations of [1, 2, 3]# and length 2comb = combinations([1, 2, 3], 2)# Print the obtained combinationsfor i in list(comb): print (i) |
Output:
(1, 2) (1, 3) (2, 3)
1. Combinations are emitted in lexicographic sort order of input. So, if the input list is sorted, the combination tuples will be produced in sorted order.
Python3
# A Python program to print all # combinations of a given length from itertools import combinations # Get all combinations of [1, 2, 3] # and length 2 comb = combinations([1, 2, 3], 2) # Print the obtained combinations for i in list(comb): print (i) |
Output:
(1, 2) (1, 3) (2, 3)
2. Elements are treated as unique based on their position, not on their value. So if the input elements are unique, there will be no repeat values in each combination.
Python3
# A Python program to print all combinations # of given length with unsorted input. from itertools import combinations # Get all combinations of [2, 1, 3] # and length 2 comb = combinations([2, 1, 3], 2) # Print the obtained combinations for i in list(comb): print (i) |
Output:
(2, 1) (2, 3) (1, 3)
3. If we want to make a combination of the same element to the same element then we use combinations_with_replacement.
Python3
# A Python program to print all combinations # with an element-to-itself combination is # also included from itertools import combinations_with_replacement # Get all combinations of [1, 2, 3] and length 2 comb = combinations_with_replacement([1, 2, 3], 2) # Print the obtained combinations for i in list(comb): print (i) |
Output:
(1, 1) (1, 2) (1, 3) (2, 2) (2, 3) (3, 3)
Permutation and Combination in Python
Python provides direct methods to find permutations and combinations of a sequence. These methods are present in itertools package.