Python – Custom Pool Sorting

Last Updated : 29 Aug, 2020

Given list and priority lists, sort the list elements on basis of their occurrence in priority lists, i.e element occurring in list1, should occur 1st and in other list should occur after that.

Input : test_list = [5, 6, 3, 7], prio1_list = [6, 3], prio2_list = [5, 7]
Output : [6, 3, 5, 7]
Explanation : 6, 3 occur in p1 list, followed by 5 and 7 which lie in p2 list.

Input : test_list = [5, 6], prio1_list = [6], prio2_list = [5]
Output : [6, 5]
Explanation : 6 occurs in 1st priority list than 5.

Method : Using sort() + comparator key function
The generic sort() can be used to perform this task. The real algorithm lies in comparator function passed in it. The assignment of appropriate return value and its order is used to solve this problem.

# Python3 code to demonstrate working of  
# Custom Pool Sorting 
# Using sort() + comparator key function 
  
# comparator function 
def func(ele): 
  
    # Returning 1 or 2 ro assign priority 
    if ele in prio1_list: 
        return  1
    elif ele in prio2_list: 
        return  2
  
# initializing list 
test_list = [5, 6, 3, 7, 4, 2, 9, 10]  
  
# printing original list 
print("The original list is : " + str(test_list)) 
  
# initializing priority lists 
prio1_list = [4, 6, 3, 8, 10] 
prio2_list = [5, 7, 1, 2, 9] 
  
# Using sort() + comparator key function 
# key passed with function to manage priority 
test_list.sort(key = func) 
  
# printing result  
print("List after sorting : " + str(test_list)) 

Output :

The original list is : [5, 6, 3, 7, 4, 2, 9, 10]
List after sorting : [6, 3, 4, 10, 5, 7, 2, 9]

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