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Hello friends and welcome to the tutorial on Sets
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{{{ Show the slide containing title }}}
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{{{ Show the slide containing the outline slide }}}
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In this tutorial, we shall learn
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* sets
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* operations on sets
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Sets are data structures which contain unique elements. In other words,
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duplicates are not allowed in sets.
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Lets look at how to input sets.
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type
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::
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a_list = [1, 2, 1, 4, 5, 6, 7]
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a = set(a_list)
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a
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We can see that duplicates are removed and the set contains only unique
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elements.
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::
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f10 = set([1, 2, 3, 5, 8])
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p10 = set([2, 3, 5, 7])
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f10 is the set of fibonacci numbers from 1 to 10.
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p10 is the set of prime numbers from 1 to 10.
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Various operations that we do on sets are possible here also.
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The | character stands for union
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::
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f10 | p10
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gives us the union of f10 and p10
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The & character stands for intersection.
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::
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f10 & p10
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gives the intersection
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similarly,
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::
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f10 - p10
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gives all the elements that are in f10 but not in p10
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::
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f10 ^ p10
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is all the elements in f10 union p10 but not in f10 intersection p10. In
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mathematical terms, it gives the symmectric difference.
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Sets also support checking of subsets.
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::
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b = set([1, 2])
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b < f10
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gives a True since b is a proper subset of f10.
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Similarly,
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::
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f10 < f10
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gives a False since f10 is not a proper subset.
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hence the right way to do would be
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::
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f10 <= f10
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and we get a True since every set is a subset of itself.
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Sets can be iterated upon just like lists and tuples.
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::
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for i in f10:
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print i,
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prints the elements of f10.
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The length and containership check on sets is similar as in lists and tuples.
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::
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len(f10)
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shows 5. And
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::
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1 in f10
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2 in f10
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prints True and False respectively
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The order in which elements are organised in a set is not to be relied upon
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since sets do not support indexing. Hence, slicing and striding are not valid
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on sets.
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{{{ Pause here and try out the following exercises }}}
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%% 1 %% Given a list of marks, marks = [20, 23, 22, 23, 20, 21, 23]
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list all the duplicates
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{{{ continue from paused state }}}
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Duplicates marks are the marks left out when we remove each element of the
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list exactly one time.
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::
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marks = [20, 23, 22, 23, 20, 21, 23]
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marks_set = set(marks)
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for mark in marks_set:
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marks.remove(mark)
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# we are now left with only duplicates in the list marks
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duplicates = set(marks)
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{{{ Show summary slide }}}
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This brings us to the end of the tutorial.
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we have learnt
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* How to make sets from lists
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* How to input sets
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* How to perform union, intersection and symmectric difference operations
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* How to check if a set is a subset of other
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* The various similarities with lists like length and containership
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{{{ Show the "sponsored by FOSSEE" slide }}}
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#[Nishanth]: Will add this line after all of us fix on one.
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This tutorial was created as a part of FOSSEE project, NME ICT, MHRD India
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Hope you have enjoyed and found it useful.
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Thankyou
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.. Author : Nishanth
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Internal Reviewer 1 :
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Internal Reviewer 2 :
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External Reviewer :
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Questions
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=========
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1. If ``a = [1, 1, 2, 3, 3, 5, 5, 8]``. What is set(a)
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a. set([1, 1, 2, 3, 3, 5, 5, 8])
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#. set([1, 2, 3, 5, 8])
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#. set([1, 2, 3, 3, 5, 5])
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#. Error
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Answer: set([1, 2, 3, 5, 8])
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2. ``a = set([1, 3, 5])``. How do you find the length of a?
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Answer: len(a)
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3. ``a = set([1, 3, 5])``. What does a[2] produce?
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a. 1
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#. 3
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#. 5
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#. Error
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Answer: Error
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4. ``odd = set([1, 3, 5, 7, 9])`` and ``squares = set([1, 4, 9, 16])``. What
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is the value of ``odd | squares``?
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Answer: set([1, 3, 4, 5, 7, 9, 16])
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5. ``odd = set([1, 3, 5, 7, 9])`` and ``squares = set([1, 4, 9, 16])``. What
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is the value of ``odd - squares``?
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Answer: set([3, 5, 7])
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6. ``odd = set([1, 3, 5, 7, 9])`` and ``squares = set([1, 4, 9, 16])``. What
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is the value of ``odd ^ squares``?
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Answer: set([3, 4, 5, 7, 16])
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7. ``odd = set([1, 3, 5, 7, 9])`` and ``squares = set([1, 4, 9, 16])``. What
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does ``odd * squares`` give?
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a. set([1, 12, 45, 112, 9])
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#. set([1, 3, 4, 5, 7, 9, 16])
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#. set([])
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#. Error
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Answer: Error
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8. ``a = set([1, 2, 3, 4])`` and ``b = set([5, 6, 7, 8])``. What is ``a + b``
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a. set([1, 2, 3, 4, 5, 6, 7, 8])
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#. set([6, 8, 10, 12])
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#. set([5, 12, 21, 32])
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#. Error
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9. ``a`` is a set. how do you check if if a varaible ``b`` exists in ``a``?
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Answer: b in a
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10. ``a`` and ``b`` are two sets. What is ``a ^ b == (a - b) | (b - a)``?
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a. True
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#. False
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Answer: False
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Problems
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========
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1. Given that mat_marks is a list of maths marks of a class. Find out the
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no.of duplicates marks in the list.
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Answer::
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unique_marks = set(mat_marks)
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no_of_duplicates = len(mat_marks) - len(unique_marks)
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2. Given that mat_marks is a list of maths marks of a class. Find how many
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duplicates of each mark exist.
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Answer::
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marks_set = set(mat_marks)
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for mark in marks_set:
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occurences = mat_marks.count(mark)
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print occurences - 1, "duplicates of", mark, "exist"
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