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- Day 7
- Set
- Creating a set
- Getting set length
- Accessing Items in set
- Checking an item
- Adding items to a list
- Removing item from a list
- Clearing item in a set
- Deleting a set
- Converting list to set
- Joining sets
- Finding intersection items
- Finding intersection items
- Checking subset and super set
- Checking difference between two sets
- Finding Symmetric difference between two sets
- Joing set
- Exercises: Day 7
- Set
Day 7
Set
Let me take you back to your elementary or high school Mathematics lesson. The Mathematics definition of set can be applied also in python. Se is a collection of unordered and unindexed distinct elements. In python set use to store unique items, and it is possible find union, intersection, difference, symmetric difference, subset, super set and disjoint set.
Creating a set
We use {} to create a set.
- Creating an empty set
# syntax
st = {}
# or
st = set()
- Creating a set with initial items
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
Example:
# syntax
fruits = {'banana', 'orange', 'mango', 'lemon'}
Getting set length
We use len() method to find the length of a set.
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
len(set)
Example:
fruits = {'banana', 'orange', 'mango', 'lemon'}
len(fruits)
Accessing Items in 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 use use in.
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
'item3' in st
Example:
fruits = {'banana', 'orange', 'mango', 'lemon'}
'mango' in fruits
Adding items to a list
Once a list is created we can not change an item but we can add additional items.
- Add one item using add()
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
st.add('item5')
Example:
fruits = {'banana', 'orange', 'mango', 'lemon'}
fruits.add('lime')
- Add multiple items or using update()
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
st.update(['item5','item6','item7'])
Example:
fruits = {'banana', 'orange', 'mango', 'lemon'}
vegetables = ('Tomato', 'Potato', 'Cabbage','Onion', 'Carrot')
fruits.update(vegetables)
Removing item from a list
We can remove an item from a list using remove() method. If the item is not found remove() method raise an errors, so it is good to check if the item exist or not. However, *discard() method doesn't raise an error.
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
st.remove('item2")
Example:
fruits = {'banana', 'orange', 'mango', 'lemon'}
fruits.pop()
Clearing item in a set
If we want to clear or empty the set we use clear method.
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
st.clear()
Example:
fruits = {'banana', 'orange', 'mango', 'lemon'}
fruits.clear()
Deleting a set
If we want to the set itself we use del operator.
# syntax
st = {'item1', 'item2', 'item3', 'item4'}
del set
Example:
fruits = {'banana', 'orange', 'mango', 'lemon'}
del fruits
Converting list to set
We can convert list to set and set to list back. Converting list to set removes duplicates and only unique items will be reserved.
# syntax
lst = ['item1', 'item2', 'item3', 'item4', 'item1']
lst = set(lst) # {'item2', 'item4', 'item1', 'item3'}
Example:
fruits = {'banana', 'orange', 'mango', 'lemon'}
del fruits
Joining sets
We can join two 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)
Example:
fruits = {'banana', 'orange', 'mango', 'lemon'}
vegetables = {'Tomato', 'Potato', 'Cabbage','Onion', 'Carrot'}
- Update This method insert an other set
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item5', 'item6', 'item7', 'item8'}
st1.update(st2)
Example:
fruits = {'banana', 'orange', 'mango', 'lemon'}
vegetables = {'Tomato', 'Potato', 'Cabbage','Onion', 'Carrot'}
Finding intersection items
Intersection returns a set of items which are in both the sets. See the example
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item3', 'item2'}
st1.intersection(st2) # {'item3', 'item2'}
Example:
whole_numbers = {0, 1, 2, 3, 4, 5, 6, 7, 8, 10}
even_numbers = {0, 2, 4, 6, 8, 10}
whole_numbers.intersection(even_numbers) # {0, 2, 4, 6, 8, 10}
python = {'p', 'y', 't', 'o','n'}
dragon = {'d', 'r', 'a', 'g', 'o','n'}
python.intersection(dragon) # {'o', 'n'}
```### Finding intersection items
Intersection returns a set of items which are in both the sets. See the example
```py
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item3', 'item2'}
st1.intersection(st2) # {'item3', 'item2'}
Example:
whole_numbers = {0, 1, 2, 3, 4, 5, 6, 7, 8, 10}
even_numbers = {0, 2, 4, 6, 8, 10}
whole_numbers.intersection(even_numbers) # {0, 2, 4, 6, 8, 10}
python = {'p', 'y', 't', 'o','n'}
dragon = {'d', 'r', 'a', 'g', 'o','n'}
python.intersection(dragon) # {'o', 'n'}
Checking subset and super set
A set can be a subset or super set of other sets:
- Subset: issubset()
- Super set: issuperset
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item2', 'item3'}
st2.issubset(st1) # True
st1.issuperset(st2) # True
Example:
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 super set
whole_numbers.issuperset(even_numbers) # True
python = {'p', 'y', 't', 'o','n'}
dragon = {'d', 'r', 'a', 'g', 'o','n'}
python.issubset(dragon) # False
Checking difference between two sets
It return the difference between the two sets.
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item2', 'item3'}
st2.difference(st1) # {'item1', 'item4'} => st1\st2
Example:
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}
python = {'p', 'y', 't', 'o','n'}
dragon = {'d', 'r', 'a', 'g', 'o','n'}
python.difference(dragon) # {'p', 'y', 't'}
dragon.difference(python) # {'d', 'r', 'a', 'g'}
Finding Symmetric difference between two sets
It return the the symmetric difference between the two sets, it means that it return a set that contains all items from both sets, except items that are present in both set, mathematically: (A\B) U (B\A)
# syntax
st1 = {'item1', 'item2', 'item3', 'item4'}
st2 = {'item2', 'item3'}
# it mean (A\B)U(B)
st2.symmetric_difference(st1) # {'item1', 'item4'}
Example:
whole_numbers = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
even_numbers = {1, 2, 3, 4, 5}
whole_numbers.symmetric_difference(even_numbers) # {0, 6, 7, 8, 9, 10}
python = {'p', 'y', 't', 'o','n'}
dragon = {'d', 'r', 'a', 'g', 'o','n'}
python.symmetric_difference(dragon) # {'r', 't', 'p', 'y', 'g', 'a', 'd'}
Joing set
If two set do not have common item or items we call it disjoint set. 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
Example:
even_numbers = {0, 2, 4 ,6, 8}
even_numbers = {1, 3, 5, 7, 9}
even_numbers.isdisjoint(odd_numbers) # True, because no common item
python = {'p', 'y', 't', 'o','n'}
dragon = {'d', 'r', 'a', 'g', 'o','n'}
python.disjoint(dragon) # False, there is common items {'o', 'n'}
Exercises: Day 7
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]
- Find the length of the set, it_companies
- Add 'Twitter' to it companies
- Insert multiple it companies at once to the set, it_companies
- Remove one of the companies from the set, it_companies
- What is the difference between remove and discard
- Join A and B
- Fin A intersection B
- Is A subset of B
- Are A and B disjoint sets
- Join A with B and B with A
- What is the symmetric difference between A and B
- Delete the sets completely
- Convert the ages to set and compare the length of the list and the set
- Explain the difference among the following data types: string, list, tuple and set