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Python | Selective Merge list every Nth position

  • Last Updated : 28 Aug, 2019

Sometimes, while working with Python list, we can come into a problem in which we need to perform merging in list. A simple merge of list is easier to perform. But sometimes, we need to handle variations in merge. One such can be merge one list with other at every Nth element. This particular problem can be faced in day-day programming and competitive programming. Let’s discuss certain way in which this task can be performed.

Method : Using loop + extend() + iter() + next()
In this method, we use a brute force approach to tackle this problem. In this we convert a larger list into an iterator and then access it’s element using next(). The whole idea behind this is faster access of elements. Smaller list is checked for every N element.




# Python3 code to demonstrate working of
# Selective Merge list every Nth position
# using loop + extend() + iter() + next()
  
# initialize lists
test_list1 = [1, 4, 9, 10, 19, 65, 78, 23, 78]
test_list2 = [8, 14, 50]
  
# printing original lists
print("The original list 1 is : " + str(test_list1))
print("The original list 2 is : " + str(test_list2))
  
# Selective Merge list every Nth position
# using loop + extend() + iter() + next()
N = 3
temp_iter = iter(test_list1)
res = []
for ele in test_list2:
    res.extend([next(temp_iter) for _ in range(N - 1)])
    res.append(ele)
res.extend(temp_iter)
  
# printing result
print("The List after merge is : " + str(res))
Output :
The original list 1 is : [1, 4, 9, 10, 19, 65, 78, 23, 78]
The original list 2 is : [8, 14, 50]
The List after merge is : [1, 4, 8, 9, 10, 14, 19, 65, 50, 78, 23, 78]

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