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436<div align="center">
<h1> 30 Days Of Python: Day 7 - Sets</h1>
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<sub>Author:
<a href="https://www.linkedin.com/in/asabeneh/" target="_blank">Asabeneh Yetayeh</a><br>
<small> Second Edition: July, 2021</small>
</sub>
</div>
[<< Day 6](../06_Day_Tuples/06_tuples.md) | [Day 8 >>](../08_Day_Dictionaries/08_dictionaries.md)
- [📘 Day 7](#-day-7)
- [Sets](#sets)
- [Creating a Set](#creating-a-set)
- [Getting Set's Length](#getting-sets-length)
- [Accessing Items in a Set](#accessing-items-in-a-set)
- [Checking an Item](#checking-an-item)
- [Adding Items to a Set](#adding-items-to-a-set)
- [Removing Items from a Set](#removing-items-from-a-set)
- [Clearing Items in a Set](#clearing-items-in-a-set)
- [Deleting a Set](#deleting-a-set)
- [Converting List to Set](#converting-list-to-set)
- [Joining Sets](#joining-sets)
- [Finding Intersection Items](#finding-intersection-items)
- [Checking Subset and Super Set](#checking-subset-and-super-set)
- [Checking the Difference Between Two Sets](#checking-the-difference-between-two-sets)
- [Finding Symmetric Difference Between Two Sets](#finding-symmetric-difference-between-two-sets)
- [Joining Sets](#joining-sets-1)
- [💻 Exercises: Day 7](#-exercises-day-7)
- [Exercises: Level 1](#exercises-level-1)
- [Exercises: Level 2](#exercises-level-2)
- [Exercises: Level 3](#exercises-level-3)
# 📘 Day 7
## Sets
Set is a collection of items. Let me take you back to your elementary or high school Mathematics lesson. The Mathematics definition of a set can be applied also in Python. Set is a collection of unordered and un-indexed distinct elements. In Python set is used to store unique items, and it is possible to find the _union_, _intersection_, _difference_, _symmetric difference_, _subset_, _super set_ and _disjoint set_ among sets.
### Creating a Set
To create an empty set, we use the set() function. Empty curly brackets {} will create a dictionary.
- Creating an empty set
```py
# syntax
st = set()
```
- Creating a set with initial items
```py
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
```
**Example:**
```py
# syntax
fruits = {'banana', 'orange', 'mango', 'lemon'}
```
### Getting Set's Length
We use **len()** method to find the length of a set.
```py
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
len(st)
```
**Example:**
```py
fruits = {'banana', 'orange', 'mango', 'lemon'}
len(fruits)
```
### Accessing Items in a Set
We use loops to access items. We will see this in loop section
### Checking an Item
To check if an item exist in a list we use _in_ membership operator.
```py
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
print("Does set st contain item3? ", 'item3' in st) # Does set st contain item3? True
```
**Example:**
```py
fruits = {'banana', 'orange', 'mango', 'lemon'}
print('mango' in fruits ) # True
```
### Adding Items to a Set
Once a set is created we cannot change any items and we can also add additional items.
- Add one item using _add()_
```py
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
st.add('item5')
```
**Example:**
```py
fruits = {'banana', 'orange', 'mango', 'lemon'}
fruits.add('lime')
```
- Add multiple items using _update()_
The _update()_ allows to add multiple items to a set. The _update()_ takes a list argument.
```py
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
st.update(['item5','item6','item7'])
```
**Example:**
```py
fruits = {'banana', 'orange', 'mango', 'lemon'}
vegetables = ('tomato', 'potato', 'cabbage','onion', 'carrot')
fruits.update(vegetables)
```
### Removing Items from a Set
We can remove an item from a set using _remove()_ method. If the item is not found _remove()_ method will raise errors, so it is good to check if the item exist in the given set. However, _discard()_ method doesn't raise any errors.
```py
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
st.remove('item2')
```
The pop() methods remove a random item from a list and it returns the removed item.
**Example:**
```py
fruits = {'banana', 'orange', 'mango', 'lemon'}
fruits.pop() # removes a random item from the set
```
If we are interested in the removed item.
```py
fruits = {'banana', 'orange', 'mango', 'lemon'}
removed_item = fruits.pop()
```
### Clearing Items in a Set
If we want to clear or empty the set we use _clear_ method.
```py
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
st.clear()
```
**Example:**
```py
fruits = {'banana', 'orange', 'mango', 'lemon'}
fruits.clear()
print(fruits) # set()
```
### Deleting a Set
If we want to delete the set itself we use _del_ operator.
```py
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
del st
```
**Example:**
```py
fruits = {'banana', 'orange', 'mango', 'lemon'}
del fruits
```
### Converting List to Set
We can convert list to set and set to list. Converting list to set removes duplicates and only unique items will be reserved.
```py
# syntax
lst = ['item1', 'item2', 'item3', 'item4', 'item1']
st = set(lst) # {'item2', 'item4', 'item1', 'item3'} - the order is random, because sets in general are unordered
```
**Example:**
```py
fruits = ['banana', 'orange', 'mango', 'lemon','orange', 'banana']
fruits = set(fruits) # {'mango', 'lemon', 'banana', 'orange'}
```
### Joining Sets
We can join two sets using the _union()_ or _update()_ method or _|_ symbol .
- Union
This method returns a new set
```py
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item5', 'item6', 'item7', 'item8'}
st3 = st1.union(st2) #st3 = st1 | st2
```
**Example:**
```py
fruits = {'banana', 'orange', 'mango', 'lemon'}
vegetables = {'tomato', 'potato', 'cabbage','onion', 'carrot'}
print(fruits.union(vegetables)) # {'lemon', 'carrot', 'tomato', 'banana', 'mango', 'orange', 'cabbage', 'potato', 'onion'}
# or using this : print(fruits | vegetables)
```
- Update
This method inserts a set into a given set
```py
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item5', 'item6', 'item7', 'item8'}
st1.update(st2) # st2 contents are added to st1
```
**Example:**
```py
fruits = {'banana', 'orange', 'mango', 'lemon'}
vegetables = {'tomato', 'potato', 'cabbage','onion', 'carrot'}
fruits.update(vegetables)
print(fruits) # {'lemon', 'carrot', 'tomato', 'banana', 'mango', 'orange', 'cabbage', 'potato', 'onion'}
```
### Finding Intersection Items
Intersection returns a set of items which are in both the sets or using _&_ symbol. See the example
```py
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item3', 'item2'}
st1.intersection(st2) # {'item3', 'item2'}
# or using thia : st1 & st2
```
**Example:**
```py
whole_numbers = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
even_numbers = {0, 2, 4, 6, 8, 10}
whole_numbers.intersection(even_numbers) # {0, 2, 4, 6, 8, 10}
python = {'p', 'y', 't', 'h', 'o','n'}
dragon = {'d', 'r', 'a', 'g', 'o','n'}
python.intersection(dragon) # {'o', 'n'}
# python & dragon
```
### Checking Subset and Super Set
A set can be a subset or super set of other sets:
- Subset: _issubset()_
- Super set: _issuperset_
```py
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item2', 'item3'}
st2.issubset(st1) # True
st1.issuperset(st2) # True
```
**Example:**
```py
whole_numbers = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
even_numbers = {0, 2, 4, 6, 8, 10}
whole_numbers.issubset(even_numbers) # False, because it is a super set
whole_numbers.issuperset(even_numbers) # True
python = {'p', 'y', 't', 'h', 'o','n'}
dragon = {'d', 'r', 'a', 'g', 'o','n'}
python.issubset(dragon) # False
```
### Checking the Difference Between Two Sets
It returns the difference between two sets or using _-_ symbol .
```py
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item2', 'item3'}
st2.difference(st1) # set() : st2 - st1
st1.difference(st2) # {'item1', 'item4'} => st1\st2 : st2 - st1
```
**Example:**
```py
whole_numbers = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
even_numbers = {0, 2, 4, 6, 8, 10}
whole_numbers.difference(even_numbers) # {1, 3, 5, 7, 9}
python = {'p', 'y', 't', 'o','n'}
dragon = {'d', 'r', 'a', 'g', 'o','n'}
python.difference(dragon) # {'p', 'y', 't'} - the result is unordered (characteristic of sets)
# python - dragon
dragon.difference(python) # {'d', 'r', 'a', 'g'}
# dragon - python
```
### Finding Symmetric Difference Between Two Sets
It returns the symmetric difference between two sets. It means that it returns a set that contains all items from both sets, except items that are present in both sets, mathematically: (A\B) ∪ (B\A)
```py
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item2', 'item3'}
# it means (A\B)∪(B\A)
st2.symmetric_difference(st1) # {'item1', 'item4'} : st2 ^ st1
```
**Example:**
```py
whole_numbers = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
some_numbers = {1, 2, 3, 4, 5}
whole_numbers.symmetric_difference(some_numbers) # {0, 6, 7, 8, 9, 10}
python = {'p', 'y', 't', 'h', 'o','n'}
dragon = {'d', 'r', 'a', 'g', 'o','n'}
python.symmetric_difference(dragon) # {'r', 't', 'p', 'y', 'g', 'a', 'd', 'h'}
# python ^ dragon
```
### Joining Sets
If two sets do not have a common item or items we call them disjoint sets. We can check if two sets are joint or disjoint using _isdisjoint()_ method.
```py
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item2', 'item3'}
st2.isdisjoint(st1) # False
```
**Example:**
```py
even_numbers = {0, 2, 4 ,6, 8}
odd_numbers = {1, 3, 5, 7, 9}
even_numbers.isdisjoint(odd_numbers) # True, because no common item
python = {'p', 'y', 't', 'h', 'o','n'}
dragon = {'d', 'r', 'a', 'g', 'o','n'}
python.isdisjoint(dragon) # False, there are common items {'o', 'n'}
```
🌕 You are a rising star . You have just completed day 7 challenges and you are 7 steps ahead in to your way to greatness. Now do some exercises for your brain and muscles.
## 💻 Exercises: Day 7
```py
# sets
it_companies = {'Facebook', 'Google', 'Microsoft', 'Apple', 'IBM', 'Oracle', 'Amazon'}
A = {19, 22, 24, 20, 25, 26}
B = {19, 22, 20, 25, 26, 24, 28, 27}
age = [22, 19, 24, 25, 26, 24, 25, 24]
```
### Exercises: Level 1
1. Find the length of the set it_companies
2. Add 'Twitter' to it_companies
3. Insert multiple IT companies at once to the set it_companies
4. Remove one of the companies from the set it_companies
5. What is the difference between remove and discard
### Exercises: Level 2
1. Join A and B
2. Find A intersection B
3. Is A subset of B
4. Are A and B disjoint sets
5. Join A with B and B with A
6. What is the symmetric difference between A and B
7. Delete the sets completely
### Exercises: Level 3
1. Convert the ages to a set and compare the length of the list and the set, which one is bigger?
2. Explain the difference between the following data types: string, list, tuple and set
3. _I am a teacher and I love to inspire and teach people._ How many unique words have been used in the sentence? Use the split methods and set to get the unique words.
🎉 CONGRATULATIONS ! 🎉
[<< Day 6](../06_Day_Tuples/06_tuples.md) | [Day 8 >>](../08_Day_Dictionaries/08_dictionaries.md)