Remove common elements in two lists [python]

Question

I want to remove the common elements between two lists. I mean something like this

name1 = ['m','a','d','d','y']

name2 = ['m','a','d','h','a','v','a','n']

#output be like

output = ['d','y','h','a','v','a','n']

Answer 1

You can do like:

import itertools

name1 = ['m','a','d','d','y']

name2 = ['m','a','d','h','a','v','a','n']

output = list(itertools.chain.from_iterable(zip(*[(x, y) for x, y in zip(name1, name2) if x != y]))) + (name2 if len(name2) > len(name1) else name1)[min(len(name1), len(name2)):]

print(output)

OUTPUT

['d', 'y', 'h', 'a', 'v', 'a', 'n']

• The list comprehension [(x, y) for x, y in zip(name1, name2) if x != y] simply compares the list character by character and stores the mismatching pairs as tuples;
• zip(* makes sure that the resulting tuples are reordered in the desired sequence (from [('d', 'h'), ('y', 'a')] for [('d', 'y'), ('h', 'a')] ;
• list(itertools.chain.from_iterable concatenates the tuples in one list;
• (name2 if len(name2) > len(name1) else name1)[min(len(name1), len(name2)):] takes the longest list and select the residual elements which have not been compared so far, attaching it to the list obtained in the previous point.

Answer 2

If order doesn't matter, you can use collections.Counter and a list comprehension:

from collections import Counter
counts = (Counter(name1) - Counter(name2)) + (Counter(name2) - Counter(name1))
out = [i for x,y in counts.items() for i in [x]*y]

Output:

['d', 'y', 'a', 'a', 'h', 'v', 'n']

Answer 3

Probably the simplest and most obvious way is to do it manually.

Example:

hi = min(len(name1), len(name2)) - 1 # last element of the shorter list

while hi >= 0:                  # iterate backwards to avoid bugs
    if name1[hi] == name2[hi]:  # check if the items in both lists are equal
        del name1[hi]           # if they are the same then delete 
        del name2[hi]           # from both lists
    hi -= 1                     # then do the same for the rest 
output = name1 + name2          # Finally merge two lists into 1