Python - Sets

What is Set?

In Python, A set is a mutable collection of distinct hashable objects, same as the list and tuple. Sets are used to store multiple items in a single variable. Each element in the set must be unique, immutable, and the sets remove the duplicate elements. Sets are mutable which means we can modify it after its creation.

A set is a collection which is both unordered and unindexed.Unlike other collections in Python, there is no index attached to the elements of the set, i.e., we cannot directly access any element of the set by the index.

Where we can use set?

We can use set when unique values needed, Since sets cannot have multiple occurrences of the same element.
It makes sets highly useful to efficiently remove duplicate values from a list or tuple.
We can use set, when we need to perform common math operations like unions and intersections.

How to create set?

It can be created by built-in function : set ( ) or by curly braces : { }

model_1 = set() # empyty set

model_2 = {1,2,3,4,5} # set of numbers

model_3 = {1,'dev',3,4,5} # set of different data types

model_4 = {"a","b","c","d","e"} # same as set(["a","b","c","d","e"])

myset = {(10,10), 10, 20} # This is also a valid set

# Not possible
# since here list is mutable
# this will cause error

my_set = {1, 2, [3, 4]}   # Invalid set-declare

Sample Program

Code - 1

Days = {"Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"}    
print(Days)    # output will be unordered
print(type(Days))

Output

{'Friday', 'Tuesday', 'Monday', 'Saturday', 'Thursday', 'Sunday', 'Wednesday'}
<class 'set'>

Code - 2

set_a = {1,2,2,3,4,4,4,5,6,7,6,8}
print(set_a) # return with only unique values

Output

{1,2,3,4,5,6,7,8}

Converting to Set

set1 = set("Devincept") # convert string to set
set2 = set((1,2,3,4,5)) # convert tuple to set
day = {1:'Monday', 2:'Tuesday'}
set3 = set(day) # convert dictionary to set

Set as Constructor

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

set_1 = set(("volvo", "bwm", "tata")) # note the double round-brackets
print(set_1)

Access Elements in a Set

You cannot simply access the elements by indexing, beacuse it is unordered set.

But you can loop through the set items using a for loop, or ask if a specified value is present in a set, by using the in keyword.

Lets look into above exapmle

set_1 = {"volvo", "bwm", "tata"}
for i in set_1:
    print(i)

To check the elements present in the set

set_1 = {"volvo", "bwm", "tata"}
print("bwm" in set_1) # True
print("Tata" in set_1) # False since python is case-sensitive.

Methods in Set

Set has some built-in function that can be used. Here we can see each method detailed through example

add()

The add() method adds an element to the set. If the element already exists, the add() method does not add the element.
```
vegetable = {'carrot','onion','beans'}
vegetable.add('potato')
print(vegetable)
```

clear()

The clear() method removes all elements in a set.

vegetable = {'carrot','onion','beans'}
vegetable.clear()
print(vegetable)

copy()

The copy() method copies the set.

vegetable = {'carrot','onion','beans'}
veg = vegetable.copy()
print(veg)

difference()

The difference() method returns a set that contains the difference between two sets.The returned set contains items that exist only in the first set, and not in both sets.
```
vegetable = {'carrot','onion','beans'}
veg = {'potato', 'pears', 'carrot'}

v = vegetable.difference(veg)
print(v)
```
difference_update()

The difference_update() method removes the items that exist in both sets.

The difference_update() method is different from the difference() method, because the difference() method returns a new set, without the unwanted items, and the difference_update() method removes the unwanted items from the original set.
```
vegetable = {'carrot','onion','beans'}
veg = {'potato', 'pears', 'carrot'}

vegetable.difference_update(veg)
print(vegetable)
```
discard()

The discard() method removes the specified item from the set.

This method is different from the remove() method, because the remove() method will raise an error if the specified item does not exist, and the discard() method will not.
```
vegetable = {'carrot','onion','beans'}
vegetable.discard('onion')
print(vegetable)
```
intersection()

The intersection() method returns a set that contains the similarity between two or more sets.

The returned set contains only items that exist in both sets, or in all sets if the comparison is done with more than two sets.
```
vegetable = {'carrot','onion','beans'}
veg = {'potato', 'pears', 'carrot'}

v = vegetable.intersection(veg)
print(v)
```
intersection_update()

The intersection_update() method removes the items that is not present in both sets (or in all sets if the comparison is done between more than two sets).

The intersection_update() method is different from the intersection() method, because the intersection() method returns a new set, without the unwanted items, and the intersection_update() method removes the unwanted items from the original set.
```
vegetable = {'carrot','onion','beans'}
veg = {'potato', 'pears', 'carrot'}

vegetable.intersection_update(veg)
print(vegetable)
```

isdisjoint()

The isdisjoint() method returns True if none of the items are present in both sets, otherwise it returns False.

vegetable = {'carrot','onion','beans'}
veg = {'potato', 'pears', 'carrot'}

v = vegetable.isdisjoint(veg)
print(v)

issubset()

The issubset() method returns True if all items in the set exists in the specified set, otherwise it retuns False.
```
x = {"a", "b", "c"}
y = {"f", "e", "d", "c", "b", "a"}

z = x.issubset(y)
print(z)
```
issupperset()

The issuperset() method returns True if all items in the specified set exists in the original set, otherwise it retuns False.
```
x = {"a", "b", "c"}
y = {"f", "e", "d", "c", "b", "a"}

z = x.issuperset(y)
print(z)
```
pop()

The pop() method removes a random item from the set.

This method returns the removed item.
```
vegetable = {'carrot','onion','beans'}
vegetable.pop('onion')
print(vegetable)
```
remove()

The remove() method removes the specified element from the set.

This method is different from the discard() method, because the remove() method will raise an error if the specified item does not exist, and the discard() method will not.
```
vegetable = {'carrot','onion','beans'}
vegetable.remove('onion')
print(vegetable)
```
union()

The union() method returns a set that contains all items from the original set, and all items from the specified set(s).

You can specify as many sets you want, separated by commas.
```
vegetable = {'carrot','onion','beans'}
veg = {'potato', 'pears', 'carrot'}

v = vegetable.union(veg)
print(v)
```

update()

The update() method updates the current set, by adding items from another set (or any other iterable).

vegetable = {'carrot','onion','beans'}
veg = {'potato', 'pears', 'carrot'}

vegetable.update(veg)
print(vegetable)

symmetric_difference()

The symmetric_difference() method returns a set that contains all items from both set, but not the items that are present in both sets.
```
vegetable = {'carrot','onion','beans'}
veg = {'potato', 'pears', 'carrot'}

v = vegetable.symmetric_difference(veg)
print(v)
```
symmetric_difference_update()

The symmetric_difference_update() method updates the original set by removing items that are present in both sets, and inserting the other items.
```
vegetable = {'carrot','onion','beans'}
veg = {'potato', 'pears', 'carrot'}

vegetable.symmetric_difference(veg)
print(vegetalbe)
```

Operators in Set

The set not only work with built-in commands but also it works with operators.

in

To check elements present in the set
```
set1 = {1,2,3,4,5}
print(2 in set1)
```
not in

To check elements not present in the set
```
set1 = {1,2,3,4,5}
print(2 not in set1)
```

To check elements present in both the sets are equal

set1 = {1,2,3,4,5}
set2 = {1,2,4,5,6}
print(set1 == set2)

To check elements present in both the sets are not equal

set1 = {1,2,3,4,5}
set2 = {1,2,4,5,6}
print(set1 != set2)

To check elements of the sets1 are less than or equal to set 2.

set1 = {1,2,3,4,5}
set2 = {1,2,4,5,6}
print(set1 <= set2)

To check elements of the sets1 are greater than set 2.

set1 = {1,2,3,4,5}
set2 = {1,2,4,5,6}
print(set1 > set2)

To get union from two sets.

set1 = {1,2,3,4,5}
set2 = {1,2,4,5,6}
set3 = set1 | set2
print(set3)

To get intersection from two sets

set1 = {1,2,3,4,5}
set2 = {1,2,4,5,6}
set3 = set1 & set2
print(set3)

The set of elements in precisely one of s1 or s2

set1 = {1,2,3,4,5}
set2 = {1,2,4,5,6}
set3 = set1 ^ set2
print(set3)

Difference between set1 and set2

set1 = {1,2,3,4,5}
set2 = {1,2,4,5,6}
set3 = set1 - set2
print(set3)

Set Vs list Vs Tuple Vs Dictionary

Set	List	Tuple	Dictionary
Set is represented by { }	List is represented by [ ]	Tuple is represented by( )	Dictionary is represented by { }
Set will not allow duplicate elements	List allows duplicate elements	Tuple allows duplicate elements	Dictionary- Set will not allow duplicate elements but keys are not duplicated
Set can use nested among all	List can use nested among all	Tuple can use nested among all	Dictonary can use nested among all
{1, 2, 3, 4, 5}	[1, 2, 3, 4, 5]	(1, 2, 3, 4, 5)	{1:'one', 2:'two', 3:'three', 4:'four', 5:'five'}
Can be created using set() function	Can be created using list() function	Can be created using tuple() function.	Can be created using dict() function.
Empty set a=set()	Empty list l=[]	Empty Tuple t=()	empty dictionary d={}
Set is unordered	List is ordered	Tuple is ordered	Dictionary is ordered
Set is mutable But elements are not duplicated.	List is mutable.	Tuple is immutabl e.	Dictionary is mutable. But Keys are not duplicated.

Additional Concept

Let's Look into something interesting and it is part of set. Let's talk about Frozen set.

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. 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.

normal_set = set(["a", "b","c"])
print(normal_set)

frozen_set = frozenset(["e", "f", "g"])
print(frozen_set)

Test your knowledge in Set

Hurray! You have learnt about Set in python. Let's get into a small test to check your understanding about sets.

Why still waiting click the link and enjoy your test.

Click - ME

Problems for Practice:

Python – Find missing and additional values in two lists.
Python program to count number of vowels using sets in given string.
Python – Check if a given string is binary string or not.
Python Set – Pairs of complete strings in two sets.
Python set to check if string is panagram.
Python program to check whether a given string is Heterogram or not
Python program to get all subsets of given size of a set.
Python – Minimum number of subsets with distinct elements using Counter.
Python – Convert a set into dictionary.
Concatenated string with uncommon characters in Python

Summary

Set is Mutable. Each elements in a set is Unordered, Immutable, Unindexed, Unique.

Declaring sets using either set() - built in function

Using curly braces set1 = {1,2,3,4,5}

Methods in sets

Method	Function
add()	Adds an element to the set
clear()	Removes all the elements from the set
copy()	Returns a copy of the set
difference()	Returns a set containing the difference between two or more sets
difference_update()	Removes the items in this set that are also included in another, specified set
discard()	Remove the specified item
intersection()	Returns a set, that is the intersection of two other sets
intersection_update()	Removes the items in this set that are not present in other, specified set(s)
isdisjoint()	Returns whether two sets have a intersection or not
issubset()	Returns whether another set contains this set or not
issuperset()	Returns whether this set contains another set or not
pop()	Removes an element from the set
remove()	Removes the specified element
union()	Return a set containing the union of sets
update()	Update the set with the union of this set and others
symmetric_difference()	Returns a set with the symmetric differences of two sets
symmetric_difference_update()	inserts the symmetric differences from this set and another

Operators in sets

Operator	Function
in	To check elements of the sets1 is present in set 2.
not in	To check elements of the sets1 is not present in set 2.
==	To check elements of the sets1 is equal set 2
!=	To check elements of the sets1 is not equal set 2
<=	To check elements of the sets1 are less than or equal to set 2
>	To check elements of the sets1 are greater than set 2
\|	To get union from two sets
&	To get intersection from two sets
^	The set of elements in precisely one of s1 or s2
-	Difference between set1 and set2

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Python - Sets

What is Set?

Where we can use set?

How to create set?

Sample Program

Code - 1

Output

Code - 2

Output

Converting to Set

Set as Constructor

Access Elements in a Set

Methods in Set

Operators in Set

Set Vs list Vs Tuple Vs Dictionary

Additional Concept

Test your knowledge in Set

Problems for Practice:

Summary

Methods in sets

Operators in sets

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Python - Sets

What is Set?

Where we can use set?

How to create set?

Sample Program

Code - 1

Output

Code - 2

Output

Converting to Set

Set as Constructor

Access Elements in a Set

Methods in Set

Operators in Set

Set Vs list Vs Tuple Vs Dictionary

Additional Concept

Test your knowledge in Set

Problems for Practice:

Summary

Methods in sets

Operators in sets