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Python – Retain K match index values from other list

  • Last Updated : 06 Mar, 2020

Sometimes, while working with Python lists, we can have a problem in which we need to retain only the strings with match a particular value from the corresponding list at same index. This can have application in many domains. Lets discuss certain ways in which this task can be performed.

Method #1 : Using list comprehension + zip()
The combination of above functionalities can be used to perform this task. In this, we extract the list after selective zipping of both the list matching K.




# Python3 code to demonstrate 
# Retain K match index values from other list
# using zip() + list comprehension
  
# Initializing lists
test_list1 = ['Gfg', 'is', 'best', 'for', 'Geeks', 'and', 'CS']
test_list2 = [4, 1, 4, 3, 4, 2, 4]
  
# printing original lists
print("The original list 1 is : " + str(test_list1))
print("The original list 2 is : " + str(test_list2))
  
# Initializing K 
K = 4
  
# Group elements from Dual List Matrix
# using zip() + list comprehension
res = [x for x, y in zip(test_list1, test_list2) if y == K]
              
# printing result 
print ("The filtered list : " + str(res))
Output :

The original list 1 is : [‘Gfg’, ‘is’, ‘best’, ‘for’, ‘Geeks’, ‘and’, ‘CS’]
The original list 2 is : [4, 1, 4, 3, 4, 2, 4]
The filtered list : [‘Gfg’, ‘best’, ‘Geeks’, ‘CS’]

Method #2 : Using compress() + list comprehension
This is yet another way in which this task can be performed. In this, we use compress() instead of zip() to solve the problem.






# Python3 code to demonstrate 
# Retain K match index values from other list
# using compress + list comprehension
from itertools import compress
  
# Initializing lists
test_list1 = ['Gfg', 'is', 'best', 'for', 'Geeks', 'and', 'CS']
test_list2 = [4, 1, 4, 3, 4, 2, 4]
  
# printing original lists
print("The original list 1 is : " + str(test_list1))
print("The original list 2 is : " + str(test_list2))
  
# Initializing K 
K = 4
  
# Group elements from Dual List Matrix
# using compress + list comprehension
res = list(compress(test_list1, map(lambda ele: ele == K, test_list2)))
              
# printing result 
print ("The filtered list : " + str(res))
Output :

The original list 1 is : [‘Gfg’, ‘is’, ‘best’, ‘for’, ‘Geeks’, ‘and’, ‘CS’]
The original list 2 is : [4, 1, 4, 3, 4, 2, 4]
The filtered list : [‘Gfg’, ‘best’, ‘Geeks’, ‘CS’]

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