Application of Sets
Another nice attribute of sets is that every value in a set is unique. This means that if you are trying to get rid of duplicates in a list, an easy way to do this is as follows:
list1 = [1,1,1,2,2,2,3,3,]
unique_list = list(set(list1))
print(unique_list)
This turns list1 into [1,2,3]
Below are some methods associated with sets
- Add to a set:
#Create the set
people = {"Richie", "Naren", "Sasha"}
# Add someone to the set
people.add("Elliott")
#print it out
print(people)
The set is now {"Richie", "Naren", "Sasha","Elliott"}
- Set unions
The union of two sets A and B is the set of elements which are in A, in B, or in both A and B. For example, if A = {1, 3, 5, 7} and B = {1, 2, 4, 6} then A ∪ B = {1, 2, 3, 4, 5, 6, 7}.
# Declare the set
people = {"Richie", "Naren", "Sasha"}
# Declare another set
vampires = {"Keenan", "Rohan"}
# See the union
population = people.union(vampires)
# print it out
print(population)
Population is now: {'Keenan', 'Naren', 'Richie', 'Rohan', 'Sasha'}
This is the same as using the | operator:
# create the sets
people = {"Richie", "Naren", "Sasha"}
vampires = {"Keenan", "Rohan"}
#see the intersections
population = people | vampires
# print it out
print(population)
- Set intersection
The intersection A ∩ B of two sets A and B is the set that contains all elements of A that also belong to B (or equivalently, all elements of B that also belong to A), but no other elements.
Form our example above, an intersect would return an empty set as there is no overlap between the values in our two sets.
Set difference
Returns a set containing all the elements of invoking set but not of the second set. We can use ‘-‘ operator here.
# Declare the sets
people = {"Richie", "Naren", "Sasha"}
vampires = {"Keenan","Sasha", "Rohan"}
# See the difference between each
safe = people – vampires
# print it out
print(safe)
Set safe will have all the elements that are in people but not vampire
Set operators
key in set # containment check
key not in set # non-containment check
s1 == s2 # set s1 is equivalent to set s2
s1 != s2 # set s1 is not equivalent to set s2
s1 | s2 # the union of set s1 and set s2
s1 & s2 # the intersection of set s1 and set s2
s1 – s2 # the set of elements in s1 but not s2
s1 ˆ s2 # the set of elements in precisely one of s1 or s2
