Python | Combine two lists alternately

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 < / code> ] 
   lst2   =   [  `a`  ,  ` b ` ,  ` c`  ]  
   print   (countList (lst1, lst2))

Exit :

 [`1`` a` `2`` b`` 3`` c`]

Python | Combine two lists alternately

Books for developers

Hands-On Machine Learning

Veracity of Big Data

Designing Data Visualizations

The Pragmatic Programmer

Submit new EBook