Sets

 

Sets

 

SET Data class is similar to that of Sets we use in Arithmetic. It is an in built Data class in python unlike in other Language. The Elements are enclosed within { and } and are unordered. The Elements can be anything which are immutable, so it can be Integer, Float, Complex , Tuple and String but not List, set or Dictionary. Though the elements of the sets should be of type immutable , individually the Set Data class is mutable. ie., we can Add or Remove elements . Indexing is not possible. That means only the whole set is referred and not the individual elements. The Set elements are unique means no repetitions of values.

 

Operators

 

Union, Intersection, Difference and Symmetric Difference are the operations that can be performed like in normal Arithmetic sets.

 

Examples

 

#set of integers

s={1,2,3,4,5}

print(s)

print(type(s))

 

#Set of Strings

s1={'a','e','i','o','u'}

print(s1)

print(type(s1))

 

s2={(1,2,3),4,(1,2)}

print(s2)

print(type(s2))

 

s3={(1,2,3),[4,5]}

print(s3)

print(type(s3))

 

Output

>>>

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

<type 'set'>

set(['a', 'i', 'e', 'u', 'o'])

<type 'set'>

set([(1, 2), 4, (1, 2, 3)])

<type 'set'>

 

It is possible to create an Empty Set. But {} does not generate an empty set it creates empty Dictionary only. Instead use set() statement to create an Empty set..

 

Add or Remove Elements

Add Method

 

Since it is unordered , indexing does not have any meaning (will generate Error). So use 'add' method to add an element.

 

s4={1,3}

print(s4)

s4.add(2)

print("After addition,the set is",s4)

 

s5={'a','u'}

print(s5)

s5.add('i')

print("After addition, the set is",s5)

 

Output

 

set([1, 3])

('After addition,the set is', set([1, 2, 3]))

set(['a', 'u'])

('After addition, the set is', set(['a', 'i', 'u']))

 

Update Method

 

Update method can be used to insert multiple values at the same time.

 

>>> s4.update((2,3,4,5))

>>> print("After update method, the set S4 is",s4)

('After update method, the set S4 is', set([1, 2, 3, 4, 5]))

 

>>> s4.update((4,5,6),(7,8,9,1))

>>> print("After update method, the set S4 is",s4)

('After update method, the set S4 is', set([1, 2, 3, 4, 5, 6, 7, 8, 9]))

 

Remove Method

 

To remove an element use Discard or Remove method. The difference between the two is while Remove method throws an error if the given element is not existing in the Set, the Discard method will not throw an error.

 

Example

 

>>> s4.discard(3)

>>> print(s4)

set([1, 2, 4, 5, 6, 7, 8, 9])

>>> s4.remove(9)

>>> print(s4)

set([1, 2, 4, 5, 6, 7, 8])

>>> s4.discard(0)

>>> print(s4)

set([1, 2, 4, 5, 6, 7, 8])

>>> s4.remove(0)

 

Traceback (most recent call last):

  File "<pyshell#17>", line 1, in <module>

    s4.remove(0)

KeyError: 0

>>> print(s4)

set([1, 2, 4, 5, 6, 7, 8])

 

The difference between Discard and Remove method is, while Discard will not throw an error if the element is not available, Remove method will throw error.

 

Operators on Set

 

Union

We can either use Union operator '|' or union() method for this. This operation combines 2 sets and removes duplicates on union.

 

Example

 

a={1,3,5,7,9}

b={2,3,5,7,11}

print(a|b)

 

Output

set([1, 2, 3, 5, 7, 9, 11])

 

Intersection

 

We can either use Intersection operator '&' or intersection() method for this. This operation combines 2 sets and gives only the common elements of the two.

 

a={1,3,5,7,9}

b={2,3,5,7,11}

print(a&b)

 

Output

set([3, 5, 7])

 

Difference

 

We can either use Difference operator '-' or difference() method for this. This operation returns a Set after removing the elements of B from A.

a={1,3,5,7,9}

b={2,3,5,7,11}

print(a-b)

 

Output

 

set([1, 9])

 

Symmetric Difference

 

We can either use Symmetric Difference operator '^' or symmetric_difference() method for this. This operation returns a Set combining the elements of A and B after removing the common elements of A and B.

 

a={1,3,5,7,9}

b={2,3,5,7,11}

print(a^b)

 

Output

set([1, 2, 9, 11])

 

Other Methods of Set

 

clear()	Removes all the elements of a set
copy()	Returns a shallow copy of a set. Creates a new Set with references to the elements in the old list
difference_update()	Removes all the elements of b in a , and is returned as a new object
intersection_update()	Returns the common elements of set A and B as a new object
pop	Another method to remove an element will be selected for removal until removed. If the Set is empty then will throw error.