Sets (in Python)

Set

• A set is a group of items where each item is unique.
• It is unordered (means there is no sequence and hence no index).
• Note: Ordered means there exists a sequence in the arrangements of grouped items. Unordered means there is no sequence.
• Ordered means that the order in which items were placed at the time of creation is maintained by the Python till no modification is done to the data itself. For ex: List and Tuple.

List Methods	Set Methods
append()	add()
extend()	update() [Note: set does not support ‘+’ op.]
remove()	remove(), discard()
pop(): removes the last element by default [Note: also accepts index to pop() an element]	pop(): we cannot say which element will be popped as a set is not ordered.
clear(): empty the list	clear(): empty the set

Intersection_update(): keeps the items in this set that are present in the other.

Now in code

Set is also a group of items in a single variable¶

Set is unordered , unindexed and can't have duplicate values¶

Set items are written in between curly brackets¶

set items are unordered, meaning: the items can appear in any order on display¶

set items are unchangeable in place ( because no index is associated with them to access )¶

We can add or remove items to and from set¶

Set can have items of mixed data type i.e - string, number , boolean and other object as well )¶

Given our knowledge about lists and tuples, let's see what we can do with sets already:¶

In [5]:

l = ['i', 'like', 'programming']
    t = ('i', 'like', 'programming')
    s = {'i', 'like', 'programming'}
    

In [6]:

print(type(l))
    print(type(t))
    print(type(s))
    

<class 'list'>
    <class 'tuple'>
    <class 'set'>
    

Duplicate values will be ignored.¶

Also, order might differ for elements in the set as a set is unordered data type.¶

In [1]:

thisset = {"apple", "banana", "cherry", "apple"}
    print(thisset)
    

{'banana', 'apple', 'cherry'}
    

thisset[0] TypeError: 'set' object is not subscriptable

A set is iterable.¶

In [2]:

for i in thisset:
        print(i)
    

banana
    apple
    cherry
    

Creating set from a list¶

In [12]:

l = ["apple", "banana", "cherry", "apple"]
    s = set(l) # Using type casting
    print(s)
    

{'cherry', 'apple', 'banana'}
    

Creating a list from a set¶

In [5]:

s = {'cherry', 'apple', 'banana'}
    l = list(s)
    print(l)
    #print(l[0:2])
    print(list(s)[0:2])
    

['banana', 'apple', 'cherry']
    ['banana', 'apple']
    

In [ ]:

In [15]:

print("guava" in s)
    

False
    

In [16]:

print("apple" in s)
    

True
    

How to remove duplicate values from a list?¶

In [2]:

x = input("enter the sentence: ").split()
    print(x)
    z = []
    y = [z.append(i) for i in x if i not in z ]
    print(z)
    

['i', 'like', 'like', 'like', 'programming']
    ['i', 'like', 'programming']
    

In [3]:

words = ['i', 'like', 'like', 'like', 'programming']
    

In [4]:

set(words)
    

Out[4]:

{'i', 'like', 'programming'}

In [1]:

x = {"apple", "banana", "cherry"}
    y = {"google", "microsoft", "apple"}
    
    x.update(y)
    
    print(x) 
    

{'apple', 'google', 'cherry', 'microsoft', 'banana'}
    

In [ ]:

Now in detail

In [80]:

# Creating a set
thisset = {"apple", "banana", "cherry", "guava"}
print(thisset)

{'banana', 'apple', 'cherry', 'guava'}
  

In [2]:

# Creating set using set constructor

thisset = set(("apple", "banana", "cherry")) # note the double round-brackets
print(thisset) 

{'banana', 'apple', 'cherry'}
  

In [3]:

# Type of Set

thisset = {"apple", "banana", "cherry"}
print(type(thisset))

<class 'set'>
  

In [1]:

# Set can't have duplicate values


set1 = {"apple", "banana", "cherry","apple"}
print(set1)

set2 = {True,2,3,False,0,"Hello",1}
print(set2) 

{'cherry', 'apple', 'banana'}
{False, True, 2, 3, 'Hello'}

Note: ( 1 & True ) and ( 0 & False ) treated as duplicate values.¶

So it would print True and False as set items but not 0 and 1.¶

In [6]:

# Set Items are unindexed

thisset = {"apple", "banana", "cherry","mango","orange","papaya"}
print(thisset[0])

  ---------------------------------------------------------------------------
  TypeError                                 Traceback (most recent call last)
  Cell In[6], line 4
        1 # Items appear in random order
        3 thisset = {"apple", "banana", "cherry","mango","orange","papaya"}
  ----> 4 print(thisset[0])
  
  TypeError: 'set' object is not subscriptable

In [12]:

# Set can have items of any type including mixed one

set1 = {"apple", "banana", "cherry"}
set2 = {1, 5, 7, 9, 3}
set3 = {True, False, False}
set4 = {True,2,3,False,0,"Hello",1} 

print(set1) # string type itmes
print(set2) # number type itmes
print(set3) # boolean type itmes
print(set4) # mixed type itmes , note ignored duplicate values 

{'banana', 'cherry', 'apple'}
  {1, 3, 5, 7, 9}
  {False, True}
  {False, True, 2, 3, 'Hello'}
  

In [8]:

# Add an item in a set 
  
  set1 = {True,False,"Hello",1}  # Note mixed data types of items
  print(set1) # True and 1 treated as duplicate values
  set1.add("Ravi")
  print(set1) # print after adding new item 'Ravi'
  

{False, True, 'Hello'}
  {False, True, 'Ravi', 'Hello'}
  

In [9]:

# Removing an item from set
  
  set1 = {True,False,"Hello",1 , "Ravi"}  # Note mixed data types of items
  print(set1) # True and 1 treated as duplicate values
  set1.remove("Ravi")
  print(set1) # print after removing item 'Ravi'
  

{False, True, 'Ravi', 'Hello'}
  {False, True, 'Hello'}
  

In [8]:

# Removing an item from set using discard built in method
  
  set1 = {True,False,"Hello",1 , "Ravi"}  # Note mixed data types of items
  print(set1) # True and 1 treated as duplicate values
  set1.discard("Hello")
  print(set1) # print after removing item 'Hello'
  

{False, True, 'Ravi', 'Hello'}
  {False, True, 'Ravi'}
  

In [9]:

# Difference between remove and discard method 
  # If item to be removed not present in set 
  # Then remove method raise an Error msg ( Key Error )
  # But discard method not raise any error message 
  
  set1 = {True,False,"Hello",1 , "Ravi"}  # Note mixed data types of items
  print(set1) # True and 1 treated as duplicate values
  set1.discard("Orange") # Note not present in set 
  print(set1)
  set1.remove("Orange") # Note not present in set 
  print(set1) 
  

{False, True, 'Ravi', 'Hello'}
  {False, True, 'Ravi', 'Hello'}
  

  ---------------------------------------------------------------------------
  KeyError                                  Traceback (most recent call last)
  Cell In[9], line 9
        7 set1.discard("Orange") # Note not present in set 
        8 print(set1)
  ----> 9 set1.remove("Orange") # Note not present in set 
       10 print(set1)
  
  KeyError: 'Orange'

In [84]:

# Removing last item from set using pop builtIn Method
  
  set1 = {"Tail","Head","Up","Top" , "Down"}  
  print(set1) 
  ItemRemoved = set1.pop() # No index passed as an argument
  print(set1) # print after removing last item , note no order exist for items 
  print("Removed Item is : " + str(ItemRemoved) )
  

{'Down', 'Up', 'Top', 'Tail', 'Head'}
  {'Up', 'Top', 'Tail', 'Head'}
  Removed Item is : Down
  

In [93]:

# Removing last item from set using pop builtIn Method
  
  set1 = {"Tail", "Head", "Up", "Top", "Down"}  
  set2 = set({}) # {} is not an empty set, it is dictionary.
  for i in range(len(set1)):
      item_removed = set1.pop()
      set2.add(item_removed)
  

In [94]:

set2
  

Out[94]:

{'Down', 'Head', 'Tail', 'Top', 'Up'}

In [92]:

x = {}
  print(type(x))
  

<class 'dict'>
  

In [14]:

# length of set
  
  thisset = {"apple", "banana", "cherry", "mango", "orange", "papaya", "apple"}
  print(len(thisset)) # Note ignore duplicate items while counting the items
  

6
  

In [15]:

# Accessing set items 
  # We cannot access items in a set by referring to an index or a key
  
  # Iterating Set items using for loop and membership operator 'in'
  
  thisset = {"apple", "banana", "cherry"}
  
  for x in thisset:
  
      print(x)
  

banana
  cherry
  apple
  

In [2]:

# Check if an item prsent or not in a set
  
  thisset = {"apple", "banana", "cherry"}
  
  print("banana" in thisset) 
  print("orange" in thisset)
  

True
  False
  

In [2]:

# To add set items in another set using built in update method

SetOne = {"apple", "banana", "cherry"}
SetTwo = {"pineapple", "mango", "papaya"}

SetOne.update(SetTwo)
print(SetOne)

{'mango', 'apple', 'cherry', 'papaya', 'pineapple', 'banana'}

In [3]:

SetOne = {"apple", "banana", "cherry"}
SetTwo = {"pineapple", "mango", "papaya"}
SetThree = SetOne + SetTwo
print(SetThree)

  ---------------------------------------------------------------------------
  TypeError                                 Traceback (most recent call last)
  /tmp/ipykernel_47615/2785294167.py in <module>
        1 SetOne = {"apple", "banana", "cherry"}
        2 SetTwo = {"pineapple", "mango", "papaya"}
  ----> 3 SetThree = SetOne + SetTwo
        4 print(SetThree)
  
  TypeError: unsupported operand type(s) for +: 'set' and 'set'

In [4]:

# Adding items of any iterable object in a set
  
  # Iterable object like : tupple , range , list 
  
  # For Ex - Adding a list items
  
  Set = {"apple", "banana", "cherry"}
  List = ["kiwi", "orange"]
  
  Set.update(List)
  print(Set)
  

{'kiwi', 'orange', 'banana', 'cherry', 'apple'}
  

In [5]:

# For Ex - Adding a tuple items
  
  Set = {"apple", "banana", "cherry"}
  Tuple = [1,2,3,"Orange",False]  # Mixted type items
  
  Set.update(Tuple)
  print(Set)
  

{False, 1, 2, 3, 'Orange', 'banana', 'cherry', 'apple'}
  

In [7]:

# For Ex - Adding a range items
  
  Set = {"apple", "banana", "cherry"}
  Range = range(0,6)
  
  Set.update(Range)
  print(Set)
  

{0, 1, 2, 3, 4, 5, 'banana', 'cherry', 'apple'}
  

In [18]:

# Empty the set 
  
  thisset = {"apple", "banana", "cherry"}
  
  thisset.clear()
  print(thisset)
  

set()
  

In [21]:

# Deleting set using del method 
  
  thisset = {"apple", "banana", "cherry"}
  
  del thisset
  print(thisset) # Try to print set items after deleting set 
  

  ---------------------------------------------------------------------------
  NameError                                 Traceback (most recent call last)
  Cell In[21], line 5
        3 thisset = {"apple", "banana", "cherry"}
        4 del thisset
  ----> 5 print(thisset)
  
  NameError: name 'thisset' is not defined

In [23]:

# Joining sets using union method
  
  # This will return a new set
  
  set1 = {"a", "b" , "c" , 1, 4 , 5}
  set2 = {1, 2, 3}
  
  set3 = set1.union(set2)
  print(set3) # Note all duplicate values ignored
  

{'b', 1, 2, 3, 4, 5, 'a', 'c'}
  

In [31]:

# Updating a set by adding items of another set
  
  set1 = {"a", "b" , "c" , 1, 4 , 5}
  set2 = {1, 2, 3}
  print(set1)
  set1.update(set2)
  print(set1) # Note all duplicate values ignored
  

{'b', 1, 'c', 4, 5, 'a'}
  {'b', 1, 2, 3, 4, 5, 'a', 'c'}
  

In [30]:

# Updating a set to have only duplicate values using intersection_update method
  
  # This will return a new set
  
  set1 = {"a", "b" , "c" , 1, 4 , 5}
  set2 = {1, 2, 3}
  print(set1)
  set1.intersection_update(set2) # Elements from set1 that are also in set2.
  print(set1) # Items of set1 after update
  

{'b', 1, 'c', 4, 5, 'a'}
  {1}
  

In [26]:

# Getting a new set of duplicate items of two sets using intersection method
  
  set1 = {"a", "b" , "c" , 1, 4 , 5}
  set2 = {1, 2, 3 , "b"}
  
  set3 = set1.intersection(set2)
  print(set3) 
  

{'b', 1}
  

In [29]:

# Geting a new set of all unique items of two sets using symmetric_difference method
  
  set1 = {"a", "b" , "c" , 1, 4 , 5}
  set2 = {1, 2, 3 , "b"}
  
  set3 = set1.symmetric_difference(set2)
  print(set3) 
  

{2, 3, 'c', 4, 5, 'a'}
  

In [32]:

# Updating a set to have all unique items using symmetric_difference_update method
  
  set1 = {"a", "b" , "c" , 1, 4 , 5}
  set2 = {1, 2, 3 , "b"}
  print(set1)
  set1.symmetric_difference_update(set2)
  print(set1) 
  

{'b', 1, 'c', 4, 5, 'a'}
  {2, 'c', 4, 5, 3, 'a'}
  

In [33]:

# Updating a set to have values which are present in the set using difference_update method
  
  set1 = {"a", "b" , "c" , 1, 2 , 3}
  set2 = {"a", "b" , "c" , "d"}
  print(set1)
  set1.difference_update(set2)
  print(set1) # Note 'd' not included in resultant set
  

{'b', 1, 2, 3, 'c', 'a'}
  {1, 2, 3}
  

In [97]:

set1 = {"a", "b" , "c" , 1, 2 , 3}
  set2 = {"a", "b" , "c" , "d"}
  print("Difference")
  print(set1 - set2)
  
  set1 = {"a", "b" , "c" , 1, 4 , 5}
  set2 = {1, 2, 3 , "b"}
  
  set3 = set1.difference(set2)
  print(set3)
  set4 = set2.difference(set1)
  print(set4)
  
  print("Symmetric Difference")
  print(set3.union(set4)) 
  

Difference
  {1, 2, 3}
  {'c', 'a', 4, 5}
  {2, 3}
  Symmetric Difference
  {2, 3, 4, 5, 'a', 'c'}
  

In [34]:

# Geting a new set to have values which are only present in the first set using difference method
  
  set1 = {"a", "b" , "c" , 1, 2 , 3}
  set2 = {"a", "b" , "c" , "d"}
  
  set3 = set1.difference(set2)
  print(set3) # Note 'd' not included in resultant set
  

{1, 2, 3}
  

In [ ]:

# Built In methods associated with set data type to perform various type operations
  
  """
  
  Method  	  Description
  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
  symmetric_difference()   	  Returns a set with the symmetric differences of two sets
  symmetric_difference_update()   	  inserts the symmetric differences from this set and another
  union()   	  Return a set containing the union of sets
  update()   	  Update the set with the union of this set and others
  
  
  
  """
  

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