Python: Set

Set

1. Introduction to Sets

Sets are data structures that, based on specific rules they define. The specific rules that are followed by sets are ‒

1) Items in a set are unique. We can not have a set that contains two items that are equal.

2) Items in a set are not ordered. Depending on the implementation, items may be sorted

using the hash of the value stored, but when you use sets you need to assume items are ordered in a random manner.

How to create a set ?

The set can be created using set function. For example ‒

>>>color=set(['red', 'green','blue'])

1. Accessing Values in Set

We cannot access the values in set using index as the set is unordered and has no index. We can display the contents of set using following python code

>>> A={10,20,30,40}

>>> print(A)

{40, 10, 20, 30}

It is also possible to iterate through each item of a set using for loop. The code is as follows

In [15]:

A = {10,20,30,40}

for i in A:

    print(i)

40

10

20

30

2. Deleting Values in Set

For removing the item from the set either remove or discard method is used. The remove() method is illustrated below‒

In [1]:

A = {10,20,30,40}

A.remove(20)

print (A)

{40, 10, 30}

Similarly we can use discard method to remove an element from the set.

In [2]:

A = {10, 20, 30, 40,50}

A.discard(30)

print (A)

{50, 20, 40, 10}

The del keyword is used to delete the set completely. The illustration of this function is as follows ‒

In [3]:

A = {10,20,30,40,50}

del A

print(A)

‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒‒

                                                                 Traceback (most recent call last)

NameError

Cell In[3], line 3

        1 A{10,20,30,40,50}

        2 del A

‒‒‒‒> 3 print(A)

NameError: name 'A' is not defined

3. Updating Values in Set

Once the set is created, we cannot change the values in the set. But we can add the element to the set.

• Using the add() method we can add the element to the set.

>>> A={10,20,30,40}

>>> A.add(25)

>>> print(A)

{40, 10, 20, 25, 30}

>>> 

• Using the update() method more than one elements can be added to the set.

>>> A={10,20,30,40}

>>> A.update([25,35,45])

>>> print(A)

{35, 40, 10, 45, 20, 25, 30}

>>> 

2. Basic Set Operations

Various set type operators in python are ‒

1) Union: The union between two sets, results in a third set with all the elements from both

sets. The union operation is performed using the operator |.

>>> a=set([1,2,3])

>>> b=set([2,3,4])

>>> c=a|b

>>> print(c) {1, 2, 3, 4}

>>> 

There exists a method named union for union of two sets. For example ‒

>>> x=set(['a','b','c'])

>>> y=set(['b','c','d'])

>>> c=x.union(y)

>>> print(c)

{'a', 'd', 'b', 'c'}

>>> 

2) Intersection: The intersection of two sets is a third set in which only common elements

from both the sets are enlisted. Intersection is performed using & operator.

For example ‒

>>> a=set([10,20,30])

>>> b=set([20,30,40])

>>> c=a&b

>>> print(c)

{20, 30}

There exists a method named intersection for intersection of two sets for example

>>> a=set([10,20,30])

>>> b=set([20,30,40])

>>> c=a.intersection(b)

>>> print(c)

{20, 30}

3) Difference: Difference of A and B i.e. (A ‒ B) is a set of elements that are only in A but not in B. Similarly, B ‒ A is a set of element in B but not in A. The operator ‒ is used for difference. Similarly the method named difference is also used for specifying the difference. For example ‒

>>> a=set([10,20,30,40,50])

>>> b=set([40,50,60,70,80])

 >>> c‒a‒b

>>> print(c)

{10, 20, 30}

>>>a.difference(b)

{10, 20, 30}

>>> 

4) Symmetric difference: Symmetric difference of A and B is a set of elements in both A

and B except those that are common in both.

Symmetric difference is performed using ^ operator. Same can be accomplished using the method symmetric_difference(). For example ‒

>>> a=set([10,20,30,40,50])

>>> b=set([40,50,60,70,80])

>>> c=a^b

>>> print(c)

{80, 20, 70, 10, 60, 30)← Note that 40 and 50 are the common elements which are not present in set c.

>>>a.symmetric_difference(b)

{80, 20, 70, 10, 60, 30}

>>> 

3. Built in Set Function

Various built in set functions are enlisted in the following table.

Function : Purpose

all() : This function return True if all elements of the set are true. This function also returns a true value is the set is empty.

any() : This function return True if any element of the set is true. If the set is empty, return False.

enumerate() : This function return an enumerate object. It contains the index and value of all the items of set as a pair.

len() : This function return the length of the set. That means it returns number of elements present in the set.

max() : This function returns the maximum value present in the set.

min() : This function returns the minimum value present in the set.

sorted() : This function returns a new sorted list from the elements.

sum() : This function returns the sum of all elements in the set.

The illustration of above functions in represented by following screenshot ‒

In [4]: A = {10,20,30,40,50)

In [5]: print(all (A))

True

In [6]:

print(any (A)).

True

In [7]: print(len(A))

5

In [8]: print(max(A))

50

In [9]:

print (min(A))

10

In [10]: print(sum(A))

150

In [11]:

B = {33,11,44,22}

print (sorted (B))

[11, 22, 33, 44]