sets.py

ls = [1, 2, 2, 5, 7]
st = {1, 2, 2, 5, 7}    # set is a collection of unique items, so it will be (1, 2, 5, 7)
                        # In python, set is an unordered collection
                        # hash table is used to store data

'''
Creating a Set
We use the set() built-in function.

Creating an empty set
'''
# syntax
st = set()
# Creating a set with initial items
# syntax
st = {'item1', 'item2', 'item3', 'item4'}


# syntax
fruits = {'banana', 'orange', 'mango', 'lemon'}

'''
Getting Set's Length
We use len() method to find the length of a set.
'''

# syntax
st = {'item1', 'item2', 'item3', 'item4'}
len(st)

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.
'''

# syntax
st = {'item1', 'item2', 'item3', 'item4'}
print("Does set st contain item3? ", 'item3' in st) # Does set st contain item3? True


fruits = {'banana', 'orange', 'mango', 'lemon'}
print('mango' in fruits ) # True


# Add one item using add()
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
st.add('item5')

fruits = {'banana', 'orange', 'mango', 'lemon'}
fruits.add('lime')

# syntax
st = {'item1', 'item2', 'item3', 'item4'}
st.update(['item5','item6','item7'])


fruits = {'banana', 'orange', 'mango', 'lemon'}
vegetables = ('tomato', 'potato', 'cabbage','onion', 'carrot')
fruits.update(vegetables)


# Removing Items from a Set
# 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.


fruits = {'banana', 'orange', 'mango', 'lemon'}
fruits.pop()  # removes a random item from the set

#If we are interested in the removed item.

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.
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
st.clear()

fruits = {'banana', 'orange', 'mango', 'lemon'}
fruits.clear()
print(fruits) # set()

# Deleting a Set
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
del st

fruits = {'banana', 'orange', 'mango', 'lemon'}
del fruits

# Converting List to Set
# syntax
lst = ['item1', 'item2', 'item3', 'item4', 'item1']
st = set(lst)  # {'item2', 'item4', 'item1', 'item3'} - the order is random, because sets in general are unordered

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.

# Union This method returns a new set
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item5', 'item6', 'item7', 'item8'}
st3 = st1.union(st2)

fruits = {'banana', 'orange', 'mango', 'lemon'}
vegetables = {'tomato', 'potato', 'cabbage','onion', 'carrot'}
print(fruits.union(vegetables)) # {'lemon', 'carrot', 'tomato', 'banana', 'mango', 'orange', 'cabbage', 'potato', 'onion'}

# Update This method inserts a set into a given set
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item5', 'item6', 'item7', 'item8'}
st1.update(st2) # st2 contents are added to st1

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

# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item3', 'item2'}
st1.intersection(st2) # {'item3', 'item2'}

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'}

# Checking Subset and Super Set

# Subset: issubset()
# Super set: issuperset
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item2', 'item3'}
st2.issubset(st1) # True
st1.issuperset(st2) # True

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

# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item2', 'item3'}
st2.difference(st1) # set()
st1.difference(st2) # {'item1', 'item4'} => st1\st2

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)
dragon.difference(python)     # {'d', 'r', 'a', 'g'}

# 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)

# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item2', 'item3'}
# it means (A\B)∪(B\A)
# it means (st1\st2)∪(st2\st1)
st2.symmetric_difference(st1) # {'item1', 'item4'}

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'}

#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.

# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item2', 'item3'}
st2.isdisjoint(st1) # False

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'}