Python | Combine two lists alternately

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Examples :

  Input:  lst1 = [1, 2, 3] lst2 = [’a’,’ b’, ’c ’]  Output:  [1,’ a’, 2, ’b’, 3,’ c’]  Input:  lst1 = [’name’,’ alice’, ’bob’] lst2 = [’ marks’, 87, 56]  Output:  [’name’,’ marks’, ’alice’, 87,’ bob’, 56] 

Method # 1: List Comprehension

# Python3 program for combining two lists
# alternatively

def countList (lst1, lst2):

return [sub [item] for item in range ( len (lst2))

for sub in [lst1, lst2]]


# Driver code

lst1 = [ 1 , 2 , 3 ]

lst2 = [ ’a’ , ’b’ , ’ c’ ]

print (countList (lst1, lst2))

Exit:

 [1, ’a’, 2,’ b’, 3, ’c’] 

There is an alternative to using list comprehension with zip (), as follows —

Method # 2: Using itertools.cycle()

def countList (lst1, lst2):

return [item for pair in zip (lst1, lst2 + [ 0 ])

for item in pair]

# Python3 program to combine two lists
# alternatively

from itertools import cycle

def countList (lst1, lst2) :

iters = [ iter (lst1), iter (lst2)]

return l ist ( iter .__ next __ () for iter in cycle (iters))


# Driver code

lst1 = [ 1 , 2 , 3 ]

lst2 = [ ’a’ , ’ b ’ , ’ c’ ]

print (countList (lst1, lst2))

Exit:

 [1, ’a’, 2,’ b’, 3, ’c’] 

Method # 3: Using reduce()

# Python3 program to combine two lists
# alternatively

import operator

from functools import reduce

def countList (lst1, lst2):

return reduce (operator.add, zip (lst1, lst2))


# Driver code

lst1 = [ 1 , 2 , 3 ]

lst2 = [ ’a’ , ’ b’ , ’c’ ]

print (countList (lst1, lst2))

Exit:

 (1, ’a’, 2,’ b’, 3, ’c’) 

Method # 4: Using the numpy

# Python3 program to combine two lists
# alternatively

import numpy as np

def countList (lst1, lst2):

return np.array ([[i, j] for i, j in zip (lst1, lst2)]). ravel ()


# Driver code

lst1 = [ 1 , 2 , 3 ]

lst2 = [ ’a’ , ’ b ’ , ’ c’ ]

print (countList (lst1, lst2))

Exit :

 [’1’’ a’ ’2’’ b’’ 3’’ c’] 

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We hope this article has helped you to resolve the problem. Apart from Python | Combine two lists alternately, check other array Python module-related topics.

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Javier Krasiko

Rome | 2023-02-07

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Davies Schteiner

Milan | 2023-02-07

Thanks for explaining! I was stuck with Python | Combine two lists alternately for some hours, finally got it done 🤗. I just hope that will not emerge anymore

Cornwall Nickolson

Boston | 2023-02-07

I was preparing for my coding interview, thanks for clarifying this - Python | Combine two lists alternately in Python is not the simplest one. Will use it in my bachelor thesis

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