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Python | Assign value to unique number in list

  • Last Updated : 28 Feb, 2019

We can assign all the numbers in a list a unique value that upon repetition it retains that value retained to it. This is a very common problem that is faced in web development when playing with id’s. Let’s discuss certain ways in which this problem can be solved.

Method #1 : Using enumerate() + list comprehension
List comprehension can be used to perform this particular task along with the enumerate function which selects the unique numbers with the help of set and former helping in the iteration in the list.

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# Python3 code to demonstrate
# assign unique value to list elements
# using list comprehension + enumerate
  
# initializing list
test_list = [1, 4, 6, 1, 4, 5, 6]
  
# printing the original list
print ("The original list is : " + str(test_list))
  
# using list comprehension + enumerate
# assign unique value to list elements 
temp = {i: j for j, i in enumerate(set(test_list))}
res = [temp[i] for i in test_list]
  
# printing result
print ("The unique value list is : " + str(res))
Output:
The original list is : [1, 4, 6, 1, 4, 5, 6]
The unique value list is : [0, 1, 3, 0, 1, 2, 3]

 
Method #2 : Using setdefault() + map() + count()
The combination of all the three function can also be used to perform this particular task. Map binds all the like elements, setdefault assigns them unique number and count function helps map to find number of total occurrences.




# Python3 code to demonstrate
# assign unique value to list elements
# using setdefault() + map() + count()
from itertools import count
  
# initializing list
test_list = [1, 4, 6, 1, 4, 5, 6]
  
# printing the original list
print ("The original list is : " + str(test_list))
  
# using setdefault() + map() + count()
# assign unique value to list elements 
res = list(map({}.setdefault, test_list, count()))
  
# printing result
print ("The unique value list is : " + str(res))
Output:
The original list is : [1, 4, 6, 1, 4, 5, 6]
The unique value list is : [0, 1, 2, 0, 1, 5, 2]



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