Create set of pairs [even,odd] combination
>>> a = { [i,j] for i in range[0,10,2] for j in range[1,10,2]}
>>> a
{[4, 7], [6, 9], [0, 7], [2, 1], [8, 9], [0, 3], [2, 5], [8, 5], [4, 9], [6, 7], [2, 9], [8, 1], [6, 3], [4, 1], [4, 5], [0, 5], [2, 3], [8, 7], [6, 5], [0, 1], [2, 7], [8, 3], [6, 1], [4, 3], [0, 9]}
def combinations[lista, listb]:
return { [i,j] for i in lista for j in listb }
>>> combinations[[1,3,5,6],[11,21,133,134,443]]
{[1, 21], [5, 133], [5, 11], [5, 134], [6, 11], [6, 134], [1, 443], [3, 11], [6, 21], [3, 21], [1, 133], [1, 134], [5, 21], [3, 134], [5, 443], [6, 443], [1, 11], [3, 443], [6, 133], [3, 133]}
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.
Input : test_list = [1, 7, 4]
Output : [[1, 7], [1, 4], [7, 4]]Input : test_list = [7, 4]
Output : [[7, 4]]
Method #1 : Using list comprehension + enumerate[]
This is one of the ways in which this task can be performed. In this, we perform the task of pairing using nested loops in list comprehension recipe, and enumerate[] is used to check with the next indices while iteration.
test_list = [1, 7, 4, 3]
print["The original list : "
+ str[test_list]]
res = [[a, b] for idx, a in enumerate[test_list] for b in test_list[idx + 1:]]
print["All possible pairs : " + str[res]]
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 combinations[]
This is one of the ways in which this task can be performed. In this, we just using inbuild function for pairing and sending 2 as value for making pairs of size 2.
from itertools import combinations
test_list = [1, 7, 4, 3]
print["The original list : " + str[test_list]]
res = list[combinations[test_list, 2]]
print["All possible pairs : " + str[res]]
Output :
The original list : [1, 7, 4, 3] All possible pairs : [[1, 7], [1, 4], [1, 3], [7, 4], [7, 3], [4, 3]]
List iteration is common in Python programming, but sometimes one requires to print the elements in consecutive pairs. This particular problem is quite common and having a solution to it always turns out to be handy. Let’s discuss certain ways in which this problem can be solved.
Pair iteration in a list using list comprehension
List comprehension can be used to print the pairs by accessing the current and next elements in the list and then printing the same. Care has to be taken while pairing the last element with the first one to form a cyclic pair.
Python3
from itertools import compress
test_list =
[0, 1, 2, 3, 4, 5]
print ["The original list is : " + str[test_list]]
res = [[[i], [i + 1] % len[test_list]]
for i in range[len[test_list]]]
print ["The pair list is : " + str[res]]
Output:
The original list is : [0, 1, 2, 3, 4, 5] The pair list is : [[0, 1], [1, 2], [2, 3], [3, 4], [4, 5], [5, 0]]
Pair iteration in a list using zip[] + list slicing
The zip function can be used to extract pairs over the list slicing can be used to successively pair the current element with the next one for efficient pairing.
Python3
from itertools import compress
test_list =
[0, 1, 2, 3, 4, 5]
print ["The original list is : " + str[test_list]]
res = list[zip[test_list, test_list[1:] + test_list[:1]]]
print ["The pair list is : " + str[res]]
Output:
The original list is : [0, 1, 2, 3, 4, 5] The pair list is : [[0, 1], [1, 2], [2, 3], [3, 4], [4, 5], [5, 0]]