Python | Difference of two lists including duplicates

Last Updated : 13 May, 2019

The ways to find difference of two lists has been discussed earlier, but sometimes, we require to remove only the specific occurrences of the elements as much they occur in other list. Let’s discuss certain ways in which this can be performed.

Method #1 : Using collections.Counter()
The Counter method can be used to get the exact occurrence of the elements in the list and hence can subtract selectively rather than using the set and ignoring the count of elements altogether. Then the subtraction can be performed to get the actual occurrence.

# Python3 code to demonstrate 
# Difference of list including duplicates 
# Using collections.Counter() 
from collections import Counter 
  
# initializing lists 
test_list1 = [1, 3, 4, 5, 1, 3, 3] 
test_list2 = [1, 3, 5] 
  
# printing original lists 
print("The original list 1 : " + str(test_list1)) 
print("The original list 2 : " + str(test_list2)) 
  
# Using collections.Counter() 
# Difference of list including duplicates 
res = list((Counter(test_list1) - Counter(test_list2)).elements()) 
  
# print result 
print("The list after performing the subtraction : " + str(res)) 

Output :

The original list 1 : [1, 3, 4, 5, 1, 3, 3]
The original list 2 : [1, 3, 5]
The list after performing the subtraction : [1, 3, 3, 4]

Method #2 : Using map() + lambda + remove()
The combination of above functions can be used to perform this particular task. The map function can be used to link the function to all elements and remove removes the first occurrence of it. Hence doesn’t remove repeatedly. Works with Python2 only.

# Python code to demonstrate 
# Difference of list including duplicates 
# Using map() + lambda + remove() 
  
# initializing lists 
test_list1 = [1, 3, 4, 5, 1, 3, 3] 
test_list2 = [1, 3, 5] 
  
# printing original lists 
print("The original list 1 : " + str(test_list1)) 
print("The original list 2 : " + str(test_list2)) 
  
# Using map() + lambda + remove() 
# Difference of list including duplicates 
res = map(lambda x: test_list1.remove(x)  
          if x in test_list1 else None, test_list2) 
  
# print result 
print("The list after performing the subtraction : " + str(test_list1)) 

Output :

The original list 1 : [1, 3, 4, 5, 1, 3, 3]
The original list 2 : [1, 3, 5]
The list after performing the subtraction : [1, 3, 3, 4]

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