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‎16-Set.py

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#Using python to manipulate sets
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'''
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A Python set is the collection of the "unordered items".
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Each element in the set must be "unique", "immutable",
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and the sets remove the duplicate elements.
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Sets are mutable which means we can modify it after its creation.
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Unlike other collections in Python, there is no index attached
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to the elements of the set, i.e., we cannot directly access
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any element of the set by the index. However, we can print
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them all together, or we can get the list of elements by
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looping through the set.
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a set is defined by a curly bracket. {}
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Sets are mutable - this means that items can be changed.
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Set has a whole bunch of methods available.
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add() Adds an element to the set
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clear() Removes all the elements from the set
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copy() Returns a copy of the set
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difference() Returns a set containing the difference between two or more sets
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difference_update() Removes the items in this set that are also included in another, specified set
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discard() Remove the specified item
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intersection() Returns a set, that is the intersection of two or more sets
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intersection_update() Removes the items in this set that are not present in other, specified set(s)
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isdisjoint() Returns whether two sets have a intersection or not
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issubset() Returns whether another set contains this set or not
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issuperset() Returns whether this set contains another set or not
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pop() Removes an element from the set
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remove() Removes the specified element
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symmetric_difference() Returns a set with the symmetric differences of two sets
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symmetric_difference_update() Inserts the symmetric differences from this set and another
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union() Return a set containing the union of sets
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update() Update the set with another set, or any other iterable
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'''
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#The basics
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basket = {'apple', 'orange', 'apple', 'pear', 'orange', 'banana'}
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print(basket)# show that duplicates have been removed
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'orange' in basket # fast membership testing TRUE
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'crabgrass' in basket # FALSE
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#Example 1
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Days = {"Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"}
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print(Days)
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print(type(Days))
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print("looping through the set elements ... ")
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for i in Days:
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print(i)
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'''
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Output
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{'Friday', 'Tuesday', 'Monday', 'Saturday', 'Thursday', 'Sunday', 'Wednesday'}
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<class 'set'>
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looping through the set elements ...
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Friday
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Tuesday
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Monday
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Saturday
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Thursday
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Sunday
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Wednesday
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'''
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'''
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It can contain any type of element such as integer, float, tuple etc.
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But mutable elements (list, dictionary, set) can't be a member of set.
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Consider the following example.
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'''
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# Creating a set which have immutable elements
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set1 = {1,2,3, "JavaTpoint", 20.5, 14}
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print(type(set1))
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#Creating a set which have mutable element
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set2 = {1,2,3,["Javatpoint",4]}
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print(type(set2))
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'''
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Output
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<class 'set'>
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Traceback (most recent call last)
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<ipython-input-5-9605bb6fbc68> in <module>
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4
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5 #Creating a set which holds mutable elements
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----> 6 set2 = {1,2,3,["Javatpoint",4]}
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7 print(type(set2))
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TypeError: unhashable type: 'list'
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In the above code, we have created two sets, the set set1 have immutable
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elements and set2 have one mutable element as a list. While checking
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the type of set2, it raised an error, which means set can contain only
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immutable elements.
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Creating an empty set is a bit different because empty curly {} braces
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are also used to create a dictionary as well. So Python provides the set()
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method used without an argument to create an empty set.
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'''
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# Empty curly braces will create dictionary
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set3 = {}
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print(type(set3))
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# Empty set using set() function
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set4 = set()
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print(type(set4))
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'''
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Output
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<class 'dict'>
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<class 'set'>
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'''
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#Adding items to the set
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'''
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Python provides the add() method and update() method which can be used
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to add some particular item to the set. The add() method is used to add a
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single element whereas the update() method is used to add multiple elements
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to the set. Consider the following example.
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'''
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#Example
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set = {"January","February"}
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set.add(""March")
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set.update({"April", "May", "June"})
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for i in set:
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print(i)
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'''
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Output
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March
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May
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February
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April
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June
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January
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'''
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#Removing items from the set
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'''
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Python provides the discard() method and remove() method
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which can be used to remove the items from the set. The difference
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between these function, using discard() function if the item does not
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exist in the set then the set remain unchanged whereas remove() method
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will through an error
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'''
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months = {"January","February", "March", "April", "May", "June"}
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print(months)
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print("\nRemoving some months from the set...")
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months.discard("January")
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months.discard("April")
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months.remove("August")
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'''
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{'March', 'May', 'February', 'April', 'June', 'January'}
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{'March', 'May', 'February', 'June'}
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Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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KeyError: 'August'
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'''
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#Python Set Operations
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'''
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Set can be performed mathematical operation such as "union",
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"intersection", "difference", and "symmetric difference".
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Python provides the facility to carry out these operations
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with operators or methods. We describe these
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operations as follows.
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'''
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#Union of two Sets
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'''The union of two sets is calculated by using the pipe (|) operator.
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or the union() function The union of the two sets contains all
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the items that are present in
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both the sets.
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'''
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#Example 1: using union | operator
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a = {"a", "b", "c", "d", "e"}
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b = {"b", "d", "f", "a", "c"}
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a|b
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#{'f', 'c', 'e', 'd', 'a', 'b'} Output
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#Intersection of two sets
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'''
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The intersection of two sets can be performed by the and & operator or
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the intersection() function. The intersection of the two sets is given as
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the set of the elements that common in both sets.
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'''
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Days1 = {"Monday","Tuesday", "Wednesday", "Thursday"}
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Days2 = {"Monday","Tuesday","Sunday", "Friday"}
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print(Days1&Days2) # {'Monday', 'Tuesday'}
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#Difference between the two sets
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'''
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The difference of two sets can be calculated by using the subtraction (-)
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operator or intersection() method. Suppose there are two sets A and B, and
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the difference is A-B that denotes the resulting set will be obtained that
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element of A, which is not present in the set B.
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'''
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Days1 = {"Monday", "Tuesday", "Wednesday", "Thursday"}
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Days2 = {"Monday", "Tuesday", "Sunday"}
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print(Days1.difference(Days2))
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#Symmetric Difference of two sets
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'''
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The symmetric difference of two sets is calculated by ^ operator or
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symmetric_difference() method. Symmetric difference of sets, it removes
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that element which is present in both sets. Consider the following example:
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'''
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a = {1,2,3,4}
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b = {1,2,9}
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c = a^b
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print(c) #{3, 4, 9}
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#Set comparisons
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'''
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Python allows us to use the comparison operators i.e., <, >, <=, >= , ==
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with the sets by using which we can check whether a set is a subset,
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superset, or equivalent to other set. The boolean true or false is
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returned depending upon the items present inside the sets.
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'''
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Days1 = {"Monday", "Tuesday", "Wednesday", "Thursday"}
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Days2 = {"Monday", "Tuesday"}
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Days3 = {"Monday", "Tuesday", "Friday"}
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#Days1 is the superset of Days2 hence it will print true.
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print (Days1>Days2)
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#prints false since Days1 is not the subset of Days2
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print (Days1<Days2)
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#prints false since Days2 and Days3 are not equivalent
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print (Days2 == Days3)

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