Efficient way to remove half of the duplicate items in a list

If order isn’t important, a way would be to get the odd or even indexes only after a sort. Those lists will be the same so you only need one of them.

l = [1,8,8,8,1,3,3,8]
l.sort()

# Get all odd indexes
odd = l[1::2]

# Get all even indexes
even = l[::2]

print(odd)
print(odd == even)

Result:

[1, 3, 8, 8]
True