Exploring the World of Sets in Python

Welcome, aspiring data scientists and coding newcomers! Today, we’re venturing into an intriguing aspect of Python that plays a pivotal role in data manipulation and analysis – sets. Python sets are powerful, versatile, and, once understood, can significantly streamline your code, especially when dealing with unique values and set operations. Let’s dive into the essence of sets, elucidating their features and functionalities with clear, practical examples.

What is a set in python?

A set is a collection type in Python, characterized by three main properties:

1. Unordered: The items in a set do not have a defined order. This means you cannot access items in a set by referring to an index or a key.
2. Mutable: You can add or remove items from a set after its creation.
3. Unique Elements: A set automatically filters out duplicate entries, leaving only unique elements.

1. Create sets

To create a set, use curly braces `{}` or the `set()` function:
Sets remove duplicate items.
Sets can handle multiple data types.

Python

# create a set from odd numbers
data = {'Red','Green','Blue',1,2,3,1.5,2.2,3.9,True,False,True}
print(data)
print(type(data))

Output

{'Red','Green','Blue',1,2,3,1.5,2.2,3.9,True,False,True}
<class 'set'>

Convert different collection data types to `sets`.

Python

# create a set from odd numbers
odd1 = [1,3,5,7,9,11,13,15,17,19,21]
odd2 = (15,17,19,21,23,25,27)       
print(odd1)
print(odd2)
# Typecast using set()
odd1=set(odd1)
odd2=set(odd2)

Output

[1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21]
(15, 17, 19, 21, 23, 25, 27)

Creating a set with duplicate items.

Python

# Create set with duplicates items during assignments
odd={1,3,5,7,1,3,5,7}
odd

Output

{1, 3, 5, 7}

Length of sets

Python

# find length of set with len()
rainbow_set={'Violet','Indigo','Blue','Green','Yellow','Orange','Red'}
len(rainbow_set)

Output

2. Access Sets

Sets don’t have indexes.
To access the elements, we can use the ‘enumerate()’ or ‘in’ operator, However, because sets are unordered, they may not be accessed in the same order in which they were saved.

Python

#  use enumerate for traversing odd1.
for _,j in enumerate(odd1):
    print(j)

Output

Python

#traverse with in operator 
for i in odd1:
    print(i)

Output

The “in” keyword can also be used to check the availability of objects.

Python

# find 11 and 12 in odd1
print(11 in odd1)
print(12 in odd1)

Output

True
False

3. Set Manipulation

add()
update()
discard()
remove()

1. `add` function

In the following example, we will be using the add function from the set class to add elements to the set. If the element you are trying to add is already in the set, then there will be no change in the set whatsoever.

`Syntax:`

setname.add(element)

Python

# use add() to add a integer in odd2
print(f'Before:{odd2}')
odd2.add(29)
print(f'After:{odd2}')

Output

Before:{15, 17, 19, 21, 23, 25, 27}
After:{15, 17, 19, 21, 23, 25, 27, 29}

There will be no change if you add an element that is already in the set. Attempting to duplicate element 15 in set odd2.

Python

# add number already present in the set
print(f'Before:{odd2}')
odd2.add(15)
print(f'After:{odd2}')

Output

Before:{15, 17, 19, 21, 23, 25, 27, 29}
After:{15, 17, 19, 21, 23, 25, 27, 29}

2. `update` function

You can add single items to a set using the `.add()` method and multiple items (from another iterable) using the `.update()` method

Syntax:

setname.update(iterable_object)

Python

# use update to add another list into set
oddlist=[x for x in range(29,40,2)]
print(f'Before:{odd2}')
odd2.update(oddlist)
print(f'After:{odd2}')

Output

Before:{15, 17, 19, 21, 23, 25, 27, 29}
After:{33, 35, 37, 39, 15, 17, 19, 21, 23, 25, 27, 29, 31}

3. `discard` function

Items can be removed using methods like `.remove()` and `.discard()`. While both remove an element from the set, `.remove()` will raise a KeyError if the element does not exist, whereas `.discard()` will not

Syntax:

setname.discard(element)

Python

# discard 49 from odd2
print(f'Before:{odd2}')
odd2.discard(49)
print(f'After:{odd2}')

Output


Before:{33, 35, 37, 39, 17, 19, 21, 23, 25, 27, 29, 31}
After:{33, 35, 37, 39, 17, 19, 21, 23, 25, 27, 29, 31}

Python

# discard 36 from odd2
print(f'Before:{odd2}')
odd2.discard(36)
print(f'After:{odd2}')

Output


Before:{33, 35, 37, 39, 17, 19, 21, 23, 25, 27, 29, 31}
After:{33, 35, 37, 39, 17, 19, 21, 23, 25, 27, 29, 31}

4. `remove` function

Use the remove method to remove an element from the set. An error will be thrown if the element you are trying to remove does not exist in the set.

Syntax:

setname.remove(element)

Python

# remove element from odd2
print(f'Before:{odd2}')
odd2.remove(15)
print(f'After:{odd2}')

Output

Before:{33, 35, 37, 39, 15, 17, 19, 21, 23, 25, 27, 29, 31}
After:{33, 35, 37, 39, 17, 19, 21, 23, 25, 27, 29, 31}

4. Set Operations

Sets in Python support mathematical set operations like union, intersection, difference, and symmetric difference. These operations can be incredibly useful in data analysis for comparing datasets.

1. union

Union with “ | “.
Union with union().

In a union of two sets, the sets are combined into a single set.

Python

# create two sets with rain and bow .
rain={'Violet','Indigo','Blue','Green','Yellow'}
bow={'Blue','Green','Yellow','Orange','Red'}
# union operator with rain and bow.
rain | bow

Output

{'Blue', 'Green', 'Indigo', 'Orange', 'Red', 'Violet', 'Yellow'}

Python

# use union() operator with rain and bow
rain.union(bow)

Output

{'Blue', 'Green', 'Indigo', 'Orange', 'Red', 'Violet', 'Yellow'}

2. Intersection

Cross-reference with ‘&’
Intersection with the function ‘intersection()’
Intersection with the function ‘intersection update()’

When two sets intersect, one set is formed from the common elements of the two sets.

Python

# intersection of rain & bow
rain & bow

Output

{'Blue', 'Green', 'Yellow'}

Python


# intersection of rain and bow
rain.intersection(bow)

Output

{'Blue', 'Green', 'Yellow'}

Python


# intersection_update of rain and bow
print(rain.intersection_update(bow))
rain

Output

None
{'Blue', 'Green', 'Yellow'}

Python

# declare colors1,colors2,colors3.
colors1={'Black','Grey','White','Brown','Blue','Red'}
colors2={'Black','Grey','White','Brown','Indigo','Purple'}
colors3={'Black','Grey','White','Brown','Blue','Red','Green','Yellow'}

# instersection_update multiple sets 
colors1.intersection_update(colors2,colors3)
print(colors1)

Output

{'Black', 'Grey', 'White', 'Brown'}

3. Difference

Distinction with -.
Distinction with difference().
Distinction with difference_update().

The difference between sets is computed by removing common element sets and selecting the remaining elements from only the first set.

Python

colors1={'Black','Grey','White','Brown','Blue','Red'}
colors2={'Black','Grey','White','Brown','Indigo','Purple'}
colors3={'Black','Grey','White','Brown','Blue','Red','Green','Yellow'}

     Input                     Output
colors1-colors2                {'Blue', 'Red'}
colors2-colors1                {'Indigo', 'Purple'}

colors3-colors2                {'Blue', 'Green', 'Red', 'Yellow'}

colors2-colors3                {'Indigo', 'Purple'}

colors1-colors3                set()

colors3-colors1                {'green','yellow'}

Difference between two sets with .difference()

Python

# difference between two sets with .difference()
print(f'{colors1}\n{colors2}')
colors1.difference(colors2)

Output

{'Brown', 'White', 'Black', 'Grey'}
{'Brown', 'Black', 'Purple', 'Indigo', 'Grey', 'White'}
set()

Difference between two sets with .difference_update()

Python


# difference between two sets with .difference_update()
print(f'{colors1}\n{colors2}')
colors1.difference_update(colors2)
print(colors1)

Output

{'Brown', 'White', 'Black', 'Grey'}
{'Brown', 'Black', 'Purple', 'Indigo', 'Grey', 'White'}
set()

4. Symmetrical Difference

symmetric distinction with ^.
Using symmetric_difference() to compute symmetric differences.

The symmetric difference is calculated by removing common elements from sets and combining them into one set.

Python

# create a set from odd numbers
data = {'Red','Green','Blue',1,2,3,1.5,2.2,3.9,True,False,True}
print(data)
print(type(data))

Output

{False, 1, 2, 3, 1.5, 2.2, 3.9, 'Blue', 'Green', 'Red'}
<class 'set'>

Symmetric Difference Using the `^` Operator

"^" The operator computes the symmetric difference between sets 1 and 2.

Python

# symmetric difference between two sets with ^ operaor
colors1^colors2

Output

{'Black', 'Brown', 'Grey', 'Indigo', 'Purple', 'White'}

Python

# symmetric difference with ^
colors2^colors3

Output

{'Black', 'Blue', 'Brown', 'Green', 'Grey', 'Red', 'White', 'Yellow'}

Python

# symmetric difference with ^
colors1^colors3

Output

{'Black', 'Blue', 'Brown', 'Green', 'Grey', 'Red', 'White', 'Yellow'}

`symmetric_difference()`

This method returns the difference between the first and second sets.

Syntax:

set1.symmetric_difference(set2)

symmetric difference between two sets with symmetric_difference()

Python

# symmetric difference between two sets with symmetric_difference()
colors1.symmetric_difference(colors2)

Output

{'Black', 'Brown', 'Grey', 'Indigo', 'Purple', 'White'}
{'Black', 'Brown', 'Grey', 'Indigo', 'Purple', 'White'}

symmetric difference between two sets with symmetric_difference()

Python

# symmetric difference between two sets with symmetric_difference()
colors2.symmetric_difference(colors1)

Output

{'Black', 'Brown', 'Grey', 'Indigo', 'Purple', 'White'}
{'Black', 'Brown', 'Grey', 'Indigo', 'Purple', 'White'}

`symmetric_difference_update()`

This method returns the difference between the first and second sets.

Syntax:

set1.symmetric_difference_update(set2).

Python

# symmetric difference between two sets with symmetric_difference_update()
print(colors1)
colors1.symmetric_difference_update(colors2)
print(colors1)

Output

set()
{'Grey', 'Brown', 'White', 'Indigo', 'Purple', 'Black'}

Python


# symmetric difference between two sets with symmetric_difference_update()
print(colors2)
colors2.symmetric_difference_update(colors3)
print(colors2)

Output

{'Brown', 'Black', 'Purple', 'Indigo', 'Grey', 'White'}
{'Blue', 'Indigo', 'Red', 'Green', 'Purple', 'Yellow'}

5. Set Comparison Operators

< lesser than
> greater than
<= lesser than equal to
>= greater than equal to
== is or is not equal to

Let’s start by making some sets for this session.

Python

num={x for x in range(10)}
odd={x for x in range(10) if x%2!=0}
even={x for x in range(10) if x%2==0}

print(num)
print(odd)
print(even)

Output

{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
{1, 3, 5, 7, 9}
{0, 2, 4, 6, 8}

In the following 4 images, there is a demonstration of all comparison operators with sets. Sets from above contain the digits 1 to 10 in num, as well as even and odd numbers from the 1 to 10 range in even and odd sets.

Python

# Is num subset of odd
num<odd

Output

False

Python

# Is  num superset of odd
num>odd

Output

True

Python

# Is subset of or equals to even
num <= even

Output

False

Python

# Is num superset of or equal to even
num >= even

Output

True

6.FrozenSet

Frozen sets are immutable, and they are made by calling the frozenset() function on a sequenced datatype.

Python

# create frozenset
num_list=[1,2,3,4,5]
num_set=frozenset(num_list )
print( num_set )

Output


frozenset({1, 2, 3, 4, 5})

Convert a tuple to frozen set.

Python

# typecast tuple to frozenset.
num_tuple=(1,2,3,4,5)
print( frozenset(num_tuple) )

Output


frozenset({1, 2, 3, 4, 5})

Convert a normal set to frozen set.

Python

# typecast set to frozenset.
num_set={1,2,3,4,5}
print( frozenset(num_set) )

Output

frozenset({1, 2, 3, 4, 5})

Convert a dictionary to frozen set, only keys will be used.

Python

# typecast dictionary to frozenset.
fict={'A':1,'B':2,'C':3,'D':4,'E':5,'F':6}
print( frozenset(fict) )

Output

frozenset({'B', 'D', 'E', 'F', 'A', 'C'})

Functions	Explanations
clear()	all items of the set are removed.
copy()	Returns a copy of the set.
isdisjoint()	Returns True if there are no common items in two sets.
issubset()	Returns True if one set is a subset of another.
issuperset()	Returns True if one set is derived from other.
pop()	Removes one element from the set at a time.
remove()	Removes the specified element from the set.