How to take two lists and combine them excluding any duplicates?

Question

I\'d like to make one list from two separate lists of unique items.

There are other similar questions but there didn\'t seem to be any that concerned doing this problem

Answer 1

Clean and professional solution:

list = [1, 2, 3]
list1 = [3, 4, 5]
result = list(set().union(list, list1)) # result [1, 2, 3, 4, 5]

Answer 2

Use a set.

>>> first = [1, 2, 3, 4]
>>> second = [3, 2, 5, 6, 7]
>>> third = list(set(first) | set(second))      # '|' is union
>>> third
[1, 2, 3, 4, 5, 6, 7]

Answer 3

A slightly more efficient way to do it:

>>> first = [1, 2, 3, 4]
>>> second = [3, 2, 5, 6, 7]

# New way
>>> list(set(first + second))
[1, 2, 3, 4, 5, 6, 7]
#1000000 loops, best of 3: 1.42 µs per loop

# Old way
>>> list(set(first) | set(second))
[1, 2, 3, 4, 5, 6, 7]
#1000000 loops, best of 3: 1.83 µs per loop

The new way is more efficient because it has only one set() instead of 2.

Answer 4

If someone want to do it without set():

a = [1,2,3]
b = [2,3,4]
newlist=[]
for i in a:
    newlist.append(i)
for z in b:
    if z not in newlist:
        newlist.append(z)
newlist.sort()
print newlist

Answer 5

>>> l1 = range(10)
>>> l2 = range(5, 15)
>>> set(l1) | set(l2)
set([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14])