Find non-common elements in lists

python algorithm list set discrete-mathematics
turtlesoup picture turtlesoup · Jul 5, 2012 · Viewed 54k times · Source

I'm trying to write a piece of code that can automatically factor an expression. For example, if I have two lists [1,2,3,4] and [2,3,5], the code should be able to find the common elements in the two lists, [2,3], and combine the rest of the elements together in a new list, being [1,4,5].

From this post: How to find list intersection? I see that the common elements can be found by 

set([1,2,3,4]&set([2,3,5]).

Is there an easy way to retrieve non-common elements from each list, in my example being [1,4] and [5]?

I can go ahead and do a for loop:

lists = [[1,2,3,4],[2,3,5]]
conCommon = []
common = [2,3]
for elem in lists:
    for elem in eachList:
    if elem not in common:
        nonCommon += elem

But this seems redundant and inefficient. Does Python provide any handy function that can do that? Thanks in advance!!

Answer

Amber picture Amber · Jul 5, 2012

Use the symmetric difference operator for sets (aka the XOR operator):

>>> set([1,2,3]) ^ set([3,4,5])
set([1, 2, 4, 5])

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