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Sort the values of first list using second list in Python

  • Difficulty Level : Medium
  • Last Updated : 25 Sep, 2020

Given two lists, sort the values of one list using the second list.
 

Examples: 

Input : list1 = ["a", "b", "c", "d", "e", "f", "g", "h", "i"]
        list2 = [ 0,   1,   1,    0,   1,   2,   2,   0,   1]

Output :['a', 'd', 'h', 'b', 'c', 'e', 'i', 'f', 'g']


Input : list1 = ["g", "e", "e", "k", "s", "f", "o", "r", "g", "e", "e", "k", "s"]
        list2 = [ 0,   1,   1,    0,   1,   2,   2,   0,   1]

Output : ['g', 'k', 'r', 'e', 'e', 'g', 's', 'f', 'o']






 

Approach : 
 

  1. Zip the two lists.
  2. Create a new, sorted list based on the zip using sorted().
  3. Using a list comprehension extract the first elements of each pair from the sorted, zipped list.

Concept : 
The purpose of zip() is to map a similar index of multiple containers so that they can be used just using as a single entity.
Below is the implementation of the above approach:
 



Python




# Python program to sort
# one list using
# the other list
 
def sort_list(list1, list2):
 
    zipped_pairs = zip(list2, list1)
 
    z = [x for _, x in sorted(zipped_pairs)]
     
    return z
     
 
# driver code
x = ["a", "b", "c", "d", "e", "f", "g", "h", "i"]
y = [ 0,   1,   1,    0,   1,   2,   2,   0,   1]
 
print(sort_list(x, y))
 
x = ["g", "e", "e", "k", "s", "f", "o", "r", "g", "e", "e", "k", "s"]
y = [ 0,   1,   1,    0,   1,   2,   2,   0,   1]
 
print(sort_list(x, y))

Output: 
 

['a', 'd', 'h', 'b', 'c', 'e', 'i', 'f', 'g']
['g', 'k', 'r', 'e', 'e', 'g', 's', 'f', 'o']






In the above code, we have two lists, the first list is being sorted with respect to the values of the second list. 
 

y = [ 0,   1,   1,    0,   1,   2,   2,   0,   1]





Here first the lowest value is checked. Like in this list, 0 is the lowest, so starting from the first index, 0 is the lowest and it is at index 0. So the value of index 0 is stored at index 0 in the first list. Similarly, 0 is again found at index 3 and so the value of index 3 in the first list is index 1. The same goes until the list is not completed.
 

Approach 2: By using Dictionary, list comprehension, lambda function

Python3




def sorting_of_element(list1,list2):
   
    # initializing blank dictionary
    f_1 = {}
     
    # initializing blank list
    final_list = []
     
    # Addition of two list in one dictionary
    f_1 = {list1[i]: list2[i] for i in range(len(list2))}
     
    # sorting of dictionary based on value
    f_lst = {k: v for k, v in sorted(f_1.items(), key=lambda item: item[1])}
     
    # Element addition in the list
    for i in f_lst.keys():
        final_list.append(i)
    return final_list
         
list1 = ["a", "b", "c", "d", "e", "f", "g", "h", "i"]
list2 = [ 0,   1,   1,    0,   1,   2,   2,   0,   1]
 
 
sorting_of_element(list1,list2)

Output:

['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i']



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