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Python | Get first element of each sublist

  • Last Updated : 06 May, 2019

Given a list of lists, write a Python program to extract first element of each sublist in the given list of lists.

Examples:

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Input : [[1, 2], [3, 4, 5], [6, 7, 8, 9]]
Output : [1, 3, 6]

Input : [['x', 'y', 'z'], ['m'], ['a', 'b'], ['u', 'v']]
Output : ['x', 'm', 'a', 'u']

 
Approach #1 : List comprehension






# Python3 program to extract first and last 
# element of each sublist in a list of lists
  
def Extract(lst):
    return [item[0] for item in lst]
      
# Driver code
lst = [[1, 2], [3, 4, 5], [6, 7, 8, 9]]
print(Extract(lst))
Output:
[1, 3, 6]

 
Approach #2 : Using zip and unpacking(*) operator

This method uses zip with * or unpacking operator which passes all the items inside the ‘lst’ as arguments to zip function. Thus, all the first element will become the first tuple of the zipped list. Returning the 0th element will thus, solve the purpose.




# Python3 program to extract first and last 
# element of each sublist in a list of lists
  
def Extract(lst):
    return list(list(zip(*lst))[0])
      
# Driver code
lst = [[1, 2], [3, 4, 5], [6, 7, 8, 9]]
print(Extract(lst))
Output:
[1, 3, 6]

Another method of using zip is given below:-




def Extract(lst):
    return list(next(zip(*lst)))

 
Approach #3 : Using itemgetter()




# Python3 program to extract first and last 
# element of each sublist in a list of lists
from operator import itemgetter
  
def Extract(lst):
    return list( map(itemgetter(0), lst ))
      
# Driver code
lst = [[1, 2], [3, 4, 5], [6, 7, 8, 9]]
print(Extract(lst))
Output:
[1, 3, 6]



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