Get unordered unique elements from two lists python

Question

if i have two lists (may be with different len):

x = [1,2,3,4]
f = [1,11,22,33,44,3,4]

result = > [11, 22, 33, 44]

doing:

for element in x:
    if element in f:
        f.remove(element)

getting

result = [11,22,33,44,4]

set method return ordered collection but i need to keep order of elements.

is there better way to do that?

Answer 1

Editing a list while iterating over it is bad practice, but here's a list comprehension to do what you want. This will keep the order as well.

>>> x = [1,2,3,4]
>>> f = [1,11,22,33,44,3,4]
>>> [a for a in f if a not in set(x)]
[11, 22, 33, 44]

Answer 2

How about set operations? This is going to generate a sorted list, which is independent to the provided order:

>>> x = [1,2,3,4]
>>> f = [1,11,22,33,44,3,4]
>>> sorted(set(f) - set(x))
[11, 22, 33, 44]

Answer 3

You should avoid removing elements of a list while looping through it. Making a copy helps.

x = [1,2,3,4]
f = [1, 11, 22, 33, 44, 3, 4]
f2 = f.copy()
for element in f2:
    if element in x:
        f.remove(element)

print(f)

Answer 4

if you iterate the list from bottom to top, you will get the correct result:

x = [1,2,3,4]
f = [1,11,22,33,44,3,4]

for i in range(len(f)-1, -1, -1):
    if f[i] in x:
        f.pop(i)        

print(f)  # [11, 22, 33, 44]

Answer 5

try this one line code, you will get the result

x = [1, 2, 3, 4]
f = [1, 11, 22, 33, 44, 3, 4]
print(sorted(set(f).difference(set(x))))

output: [11, 22, 33, 44]