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pythonlistsetdifference

How to create a new set of all elements that are in only one of multiple sets?

I need the code to:

  1. scan all elements of four different sets
  2. put values that only appear uniquely in one set and not the others inside a new set

Example:

A{1,2,3,4,5}

B{1,2,3,4,6}

C{1,3,4,7}

D{1,8,9}

Set E would look like: {5,6,7,8,9}

Solution

  • How about pooling all the sets (allowing for duplicates), counting the elements, and then take elements that occur only once?

    import itertools
import collections

A = {1,2,3,4,5}
B = {1,2,3,4,6}
C = {1,3,4,7}
D = {1,8,9}

cnt = collections.Counter(itertools.chain(A, B, C, D))
E = {k for k, v in cnt.items() if v == 1}
print(E) # {5, 6, 7, 8, 9}

    If you are somewhat reluctant to import modules, the following is equivalent:

    A = {1,2,3,4,5}
B = {1,2,3,4,6}
C = {1,3,4,7}
D = {1,8,9}

cnt = {} # prepare an empty list
for s in [A, B, C, D]: # loop over sets
    for x in s: # for each element in set s
        cnt[x] = cnt.get(x, 0) + 1 # increment the counter

E = set(k for k, v in cnt.items() if v == 1) # set consisting of singleton elements
print(E) # {5, 6, 7, 8, 9}