Sets

 Sets in Python

A Set in Python is used to store a collection of items with the following properties.

·        No duplicate elements. If try to insert the same item again, it overwrites previous one.

·        An unordered collection. When we access all items, they are accessed without any specific order and we cannot access items using indexes as we do in lists.

·        Internally use hashingSets in Python

A Set in Python is used to store a collection of items with the following properties.

·        No duplicate elements. If try to insert the same item again, it overwrites previous one.

·        An unordered collection. When we access all items, they are accessed without any specific order and we cannot access items using indexes as we do in lists.

·        Internally use hashing that makes set efficient for search, insert and delete operations. It gives a major advantage over a list for problems with these operations.

·        Mutable, meaning we can add or remove elements after their creation, the individual elements within the set cannot be changed directly.

Example of Python Sets

s = {10, 50, 20}

print(s)

print(type(s))

Type Casting with Python Set method

The Python set() method is used for type casting.

# typecasting list to set

s = set(["a", "b", "c"])

print(s)

# Adding element to the set

s.add("d")

print(s)

Check unique and  Immutable with Python Set

Python sets cannot have duplicate values. While you cannot modify the individual elements directly, you can still add or remove elements from the set.

# Python program to demonstrate that

# a set cannot have duplicate values 

# and we cannot change its items

# a set cannot have duplicate values

s = {"Geeks", "for", "Geeks"}

print(s)

# values of a set cannot be changed

s[1] = "Hello"

print(s)

Heterogeneous Element with Python Set

Python sets can store heterogeneous elements in it, i.e., a set can store a mixture of string, integer, boolean, etc datatypes.

# Python example demonstrate that a set

# can store heterogeneous elements

s = {"Geeks", "for", 10, 52.7, True}

print(s)

Python Frozen Sets

Frozen sets in Python 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. It can be done with frozenset() method in Python.

While elements of a set can be modified at any time, elements of the frozen set remain the same after creation. 

If no parameters are passed, it returns an empty frozenset.

# Python program to demonstrate differences

# between normal and frozen set

# Same as {"a", "b","c"}

s = set(["a", "b","c"])

print("Normal Set")

print(s)

# A frozen set

fs = frozenset(["e", "f", "g"])

print("\nFrozen Set")

print(fs)

# Uncommenting below line would cause error as

# we are trying to add element to a frozen set

# fs.add("h")

Methods for Sets

Adding elements to Python Sets

Insertion in the set is done through the set.add() function, where an appropriate record value is created to store in the hash table. Same as checking for an item, i.e., O(1) on average. However, in worst case it can become O(n).

# A Python program to

# demonstrate adding elements

# in a set

# Creating a Set

people = {"Jay", "Idrish", "Archi"}

print("People:", end = " ")

print(people)

# This will add Daxit

# in the set

people.add("Daxit")

# Adding elements to the

# set using iterator

for i in range(1, 6):

    people.add(i)

print("\nSet after adding element:", end = " ")

print(people)

Union operation on Python Sets

Two sets can be merged using union() function or | operator. Both Hash Table values are accessed and traversed with merge operation perform on them to combine the elements, at the same time duplicates are removed. The Time Complexity of this is O(len(s1) + len(s2)) where s1 and s2 are two sets whose union needs to be done.

# Python Program to

# demonstrate union of

# two sets

people = {"Jay", "Idrish", "Archil"}

vampires = {"Karan", "Arjun"}

dracula = {"Deepanshu", "Raju"}

# Union using union()

# function

population = people.union(vampires)

print("Union using union() function")

print(population)

# Union using "|"

# operator

population = people|dracula

print("\nUnion using '|' operator")

print(population)

Intersection operation on Python Sets

This can be done through intersection() or & operator. Common Elements are selected. They are similar to iteration over the Hash lists and combining the same values on both the Table. Time Complexity of this is O(min(len(s1), len(s2)) where s1 and s2 are two sets whose union needs to be done.

# Python program to

# demonstrate intersection

# of two sets

set1 = set()

set2 = set()

for i in range(5):

    set1.add(i)

for i in range(3,9):

    set2.add(i)

# Intersection using

# intersection() function

set3 = set1.intersection(set2)

print("Intersection using intersection() function")

print(set3)

# Intersection using

# "&" operator

set3 = set1 & set2

print("\nIntersection using '&' operator")

print(set3)

Finding Differences of Sets in Python

To find differences between sets. Similar to finding differences in the linked list. This is done through difference() or – operator. Time complexity of finding difference s1 – s2 is O(len(s1))

# Python program to

# demonstrate difference

# of two sets

set1 = set()

set2 = set()

for i in range(5):

    set1.add(i)

for i in range(3,9):

    set2.add(i)

# Difference of two sets

# using difference() function

set3 = set1.difference(set2)

print(" Difference of two sets using difference() function")

print(set3)

# Difference of two sets

# using '-' operator

set3 = set1 - set2

print("\nDifference of two sets using '-' operator")

print(set3)

Clearing Python Sets

Set Clear() method empties the whole set inplace.

# Python program to

# demonstrate clearing

# of set

set1 = {1,2,3,4,5,6}

print("Initial set")

print(set1)

# This method will remove

# all the elements of the set

set1.clear()

print("\nSet after using clear() function")

print(set1)

Get the Length of a Set

To determine how many items a set has, use the len() function.

thisset = {"apple", "banana", "cherry"}



print(len(thisset))

type()

From Python's perspective, sets are defined as objects with the data type 'set':

<class 'set'>

Example

myset = {"apple", "banana", "cherry"}

print(type(myset))

The set() Constructor

It is also possible to use the set() constructor to make a set.

Example

#Using the set() constructor to make a set:

thisset = set(("apple", "banana", "cherry")) # note the double round-brackets

print(thisset)

The set() Constructor

It is also possible to use the set() constructor to make a set.

Example

#Using the set() constructor to make a set:

thisset = set(("apple", "banana", "cherry")) # note the double round-brackets

print(thisset)

Operators for Sets

Sets and frozen sets support the following operators:

Operators	Notes
key in s	containment check
key not in s	non-containment check
s1 == s2	s1 is equivalent to s2
s1 != s2	s1 is not equivalent to s2
s1 <= s2	s1 is subset of s2
s1 < s2	s1 is proper subset of s2
s1 >= s2	s1 is superset of s2
s1 > s2	s1 is proper superset of s2
s1 | s2	the union of s1 and s2
s1 & s2	the intersection of s1 and 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

  that makes set efficient for search, insert and delete operations. It gives a major advantage over a list for problems with these operations.

·        Mutable, meaning we can add or remove elements after their creation, the individual elements within the set cannot be changed directly.

Example of Python Sets

s = {10, 50, 20}

print(s)

print(type(s))

Type Casting with Python Set method

The Python set() method is used for type casting.

# typecasting list to set

s = set(["a", "b", "c"])

print(s)

# Adding element to the set

s.add("d")

print(s)

Check unique and  Immutable with Python Set

Python sets cannot have duplicate values. While you cannot modify the individual elements directly, you can still add or remove elements from the set.

# Python program to demonstrate that

# a set cannot have duplicate values 

# and we cannot change its items

# a set cannot have duplicate values

s = {"Geeks", "for", "Geeks"}

print(s)

# values of a set cannot be changed

s[1] = "Hello"

print(s)

Heterogeneous Element with Python Set

Python sets can store heterogeneous elements in it, i.e., a set can store a mixture of string, integer, boolean, etc datatypes.

# Python example demonstrate that a set

# can store heterogeneous elements

s = {"Geeks", "for", 10, 52.7, True}

print(s)

Python Frozen Sets

Frozen sets in Python 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. It can be done with frozenset() method in Python.

While elements of a set can be modified at any time, elements of the frozen set remain the same after creation. 

If no parameters are passed, it returns an empty frozenset.

# Python program to demonstrate differences

# between normal and frozen set

# Same as {"a", "b","c"}

s = set(["a", "b","c"])

print("Normal Set")

print(s)

# A frozen set

fs = frozenset(["e", "f", "g"])

print("\nFrozen Set")

print(fs)

# Uncommenting below line would cause error as

# we are trying to add element to a frozen set

# fs.add("h")

Methods for Sets

Adding elements to Python Sets

Insertion in the set is done through the set.add() function, where an appropriate record value is created to store in the hash table. Same as checking for an item, i.e., O(1) on average. However, in worst case it can become O(n).

# A Python program to

# demonstrate adding elements

# in a set

# Creating a Set

people = {"Jay", "Idrish", "Archi"}

print("People:", end = " ")

print(people)

# This will add Daxit

# in the set

people.add("Daxit")

# Adding elements to the

# set using iterator

for i in range(1, 6):

    people.add(i)

print("\nSet after adding element:", end = " ")

print(people)

Union operation on Python Sets

Two sets can be merged using union() function or | operator. Both Hash Table values are accessed and traversed with merge operation perform on them to combine the elements, at the same time duplicates are removed. The Time Complexity of this is O(len(s1) + len(s2)) where s1 and s2 are two sets whose union needs to be done.

# Python Program to

# demonstrate union of

# two sets

people = {"Jay", "Idrish", "Archil"}

vampires = {"Karan", "Arjun"}

dracula = {"Deepanshu", "Raju"}

# Union using union()

# function

population = people.union(vampires)

print("Union using union() function")

print(population)

# Union using "|"

# operator

population = people|dracula

print("\nUnion using '|' operator")

print(population)

Intersection operation on Python Sets

This can be done through intersection() or & operator. Common Elements are selected. They are similar to iteration over the Hash lists and combining the same values on both the Table. Time Complexity of this is O(min(len(s1), len(s2)) where s1 and s2 are two sets whose union needs to be done.

# Python program to

# demonstrate intersection

# of two sets

set1 = set()

set2 = set()

for i in range(5):

    set1.add(i)

for i in range(3,9):

    set2.add(i)

# Intersection using

# intersection() function

set3 = set1.intersection(set2)

print("Intersection using intersection() function")

print(set3)

# Intersection using

# "&" operator

set3 = set1 & set2

print("\nIntersection using '&' operator")

print(set3)

Finding Differences of Sets in Python

To find differences between sets. Similar to finding differences in the linked list. This is done through difference() or – operator. Time complexity of finding difference s1 – s2 is O(len(s1))

# Python program to

# demonstrate difference

# of two sets

set1 = set()

set2 = set()

for i in range(5):

    set1.add(i)

for i in range(3,9):

    set2.add(i)

# Difference of two sets

# using difference() function

set3 = set1.difference(set2)

print(" Difference of two sets using difference() function")

print(set3)

# Difference of two sets

# using '-' operator

set3 = set1 - set2

print("\nDifference of two sets using '-' operator")

print(set3)

Clearing Python Sets

Set Clear() method empties the whole set inplace.

# Python program to

# demonstrate clearing

# of set

set1 = {1,2,3,4,5,6}

print("Initial set")

print(set1)

# This method will remove

# all the elements of the set

set1.clear()

print("\nSet after using clear() function")

print(set1)

Get the Length of a Set

To determine how many items a set has, use the len() function.

thisset = {"apple", "banana", "cherry"}

print(len(thisset))

type()

From Python's perspective, sets are defined as objects with the data type 'set':

<class 'set'>

Example

myset = {"apple", "banana", "cherry"}

print(type(myset))

The set() Constructor

It is also possible to use the set() constructor to make a set.

Example

#Using the set() constructor to make a set:

thisset = set(("apple", "banana", "cherry")) # note the double round-brackets

print(thisset)

The set() Constructor

It is also possible to use the set() constructor to make a set.

Example

#Using the set() constructor to make a set:

thisset = set(("apple", "banana", "cherry")) # note the double round-brackets

print(thisset)

Operators for Sets

Sets and frozen sets support the following operators:

Operators	Notes
key in s	containment check
key not in s	non-containment check
s1 == s2	s1 is equivalent to s2
s1 != s2	s1 is not equivalent to s2
s1 <= s2	s1 is subset of s2
s1 < s2	s1 is proper subset of s2
s1 >= s2	s1 is superset of s2
s1 > s2	s1 is proper superset of s2
s1 | s2	the union of s1 and s2
s1 & s2	the intersection of s1 and 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