Python | Combine two lists alternately

Michael Zippo 18.07.2021

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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