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Python – Cross Pattern Pairs in List

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  • Last Updated : 11 Oct, 2020

Given two lists, pair them diagonally, in cross pattern [works for even and equi-length lists].

Input : test_list1 = [4, 5, 6, 2], test_list2 = [9, 1, 4, 7] 
Output : [(4, 1), (5, 9), (6, 7), (2, 4)] 
Explanation : Crosslinked diagonally, 4->1, 5->9.

Input : test_list1 = [4, 5], test_list2 = [9, 1] 
Output : [(4, 1), (5, 9)] 
Explanation : Crosslinked diagonally, 4->1, 5->9. 
 

Method #1 : Using loop

In this, we iterate through list and test for even or odd index, in case of even index, we pair with next element of other list, or else we pair with previous element of other list. This way cross pattern tuples are formed.

Python3




# Python3 code to demonstrate working of
# Cross Pattern Pairs in List
# Using loop
  
  
# function to generate cross pattern pairs
def crossPair(test_list1, test_list2):
  
    # lengths of both lists should be equal
    if len(test_list1) != len(test_list2):
        return -1
  
    res = []
    for idx in range(len(test_list1)):
  
        # checking for conditions
        if idx % 2 == 0:
            res.append((test_list1[idx], test_list2[idx + 1]))
        else:
            res.append((test_list1[idx], test_list2[idx - 1]))
    return res
  
  
# initializing lists
input_list1 = [4, 5, 6, 2, 8, 9]
input_list2 = [9, 1, 4, 7, 9, 2]
  
# printing original lists
print("The original list 1 is : " + str(input_list1))
print("The original list 2 is : " + str(input_list2))
  
# printing result
print("Paired List elements : ", crossPair(input_list1, input_list2))

Output:

The original list 1 is : [4, 5, 6, 2, 8, 9]
The original list 2 is : [9, 1, 4, 7, 9, 2]
Paired List elements :  [(4, 1), (5, 9), (6, 7), (2, 4), (8, 2), (9, 9)]

Method #2 : Using list comprehension

Uses similar approach as above method, difference being list comprehension is used as a single linear alternative to solve this problem.

Python3




# Python3 code to demonstrate working of
# Cross Pattern Pairs in List
# Using list comprehension
  
  
# function to generate cross pattern pairs
def crossPair(test_list1, test_list2):
  
    # lengths of both lists should be equal
    if len(test_list1) != len(test_list2):
        return -1
  
    # list comprehension used as one liner alternative
    res = [(test_list1[idx], test_list2[idx + 1]) if idx % 2 ==
           0 else (test_list1[idx], test_list2[idx - 1]) for idx in range(len(test_list1))]
    return res
  
  
# initializing lists
input_list1 = [4, 5, 6, 2, 8, 9]
input_list2 = [9, 1, 4, 7, 9, 2]
  
# printing original lists
print("The original list 1 is : " + str(input_list1))
print("The original list 2 is : " + str(input_list2))
  
# printing result
print("Paired List elements : ", crossPair(input_list1, input_list2))

Output:

The original list 1 is : [4, 5, 6, 2, 8, 9]
The original list 2 is : [9, 1, 4, 7, 9, 2]
Paired List elements :  [(4, 1), (5, 9), (6, 7), (2, 4), (8, 2), (9, 9)]


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