Python | Get first element of each sublist
Given a list of lists, write a Python program to extract first element of each sublist in the given list of lists.
Examples:
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]
Last Updated on November 13, 2021 by admin