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Set

  • Set doesn't support indexing/slicing
  • Set doesn't support random.choices(a), since it doesn't support indexing
  • Implementation is mostly similar to dictionary

A Set is an unordered collection data type that is iterable, mutable, and has no duplicate elements. Python's set class represents the mathematical notion of a set. The major advantage of using a set, as opposed to a list, is that it has a highly optimized method for checking whether a specific element is contained in the set. This is based on a data structure known as a hash table.

Frozen Sets​

Frozen sets are immutable objects that only support methods and operators that produce a result without affecting the frozen set or sets to which they are applied

Creating a set​

A set is created by using the set() function or placing all the elements within a pair of curly braces.

Days=set(["Mon","Tue","Wed","Thu","Fri","Sat","Sun"])
Months={"Jan","Feb","Mar"}
Dates={21,22,17}

Adding element to set​

Days.add("Sun")

Removing item to set​

Days.discard("Sun")

Union of sets​

The set of elements in A, B or both (written as A | B)

DaysA = set(["Mon","Tue","Wed"])
DaysB = set(["Wed","Thu","Fri","Sat","Sun"])
AllDays = DaysA|DaysB

set(['Wed', 'Fri', 'Tue', 'Mon', 'Thu', 'Sat'])

Intersection of sets​

The set of elements in both A and B (written as A & B)

DaysA = set(["Mon","Tue","Wed"])
DaysB = set(["Wed","Thu","Fri","Sat","Sun"])
AllDays = DaysA & DaysB

set(['Wed'])

Difference of sets​

The set of elements in A but not in B (written as A - B)

The order matters for Difference. A - B is NOT the same as B - A.

DaysA = set(["Mon","Tue","Wed"])
DaysB = set(["Wed","Thu","Fri","Sat","Sun"])
AllDays = DaysA - DaysB

set(['Mon', 'Tue'])

# or
AllDays = DaysA.difference(DaysB) # for A - B
AllDaysB = DaysB.difference(DaysA) # for B - A

Python Set | difference() - GeeksforGeeks

Symmetric Difference​

The set of elements in either A or B but not both A and B (written as A ^ B)

DaysA = set(["Mon","Tue","Wed"])
DaysB = set(["Wed","Thu","Fri","Sat","Sun"])
AllDays = DaysA ^ DaysB

set(['Fri', 'Mon', 'Sat', 'Sun', 'Thu', 'Tue'])

Compare Sets​

We can check if a given set is a subset or superset of another set. The result is True or False depending on the elements present in the sets.

DaysA = set(["Mon","Tue","Wed"])
DaysB = set(["Mon","Tue","Wed","Thu","Fri","Sat","Sun"])
SubsetRes = DaysA <= DaysB
SupersetRes = DaysB >= DaysA
print(SubsetRes)
print(SupersetRes)

True
True