diff -r da873a5ac918 -r ab748264f726 sets.rst --- a/sets.rst Thu Oct 07 14:10:32 2010 +0530 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000 @@ -1,240 +0,0 @@ -Hello friends and welcome to the tutorial on Sets - -{{{ Show the slide containing title }}} - -{{{ Show the slide containing the outline slide }}} - -In this tutorial, we shall learn - - * sets - * operations on sets - -Sets are data structures which contain unique elements. In other words, -duplicates are not allowed in sets. - -Lets look at how to input sets. -type -:: - - a_list = [1, 2, 1, 4, 5, 6, 7] - a = set(a_list) - a - -We can see that duplicates are removed and the set contains only unique -elements. -:: - - f10 = set([1, 2, 3, 5, 8]) - p10 = set([2, 3, 5, 7]) - -f10 is the set of fibonacci numbers from 1 to 10. -p10 is the set of prime numbers from 1 to 10. - -Various operations that we do on sets are possible here also. -The | character stands for union -:: - - f10 | p10 - -gives us the union of f10 and p10 - -The & character stands for intersection. -:: - - f10 & p10 - -gives the intersection - -similarly, -:: - - f10 - p10 - -gives all the elements that are in f10 but not in p10 - -:: - - f10 ^ p10 - -is all the elements in f10 union p10 but not in f10 intersection p10. In -mathematical terms, it gives the symmectric difference. - -Sets also support checking of subsets. -:: - - b = set([1, 2]) - b < f10 - -gives a True since b is a proper subset of f10. -Similarly, -:: - - f10 < f10 - -gives a False since f10 is not a proper subset. -hence the right way to do would be -:: - - f10 <= f10 - -and we get a True since every set is a subset of itself. - -Sets can be iterated upon just like lists and tuples. -:: - - for i in f10: - print i, - -prints the elements of f10. - -The length and containership check on sets is similar as in lists and tuples. -:: - - len(f10) - -shows 5. And -:: - - 1 in f10 - 2 in f10 - -prints True and False respectively - -The order in which elements are organised in a set is not to be relied upon -since sets do not support indexing. Hence, slicing and striding are not valid -on sets. - -{{{ Pause here and try out the following exercises }}} - -%% 1 %% Given a list of marks, marks = [20, 23, 22, 23, 20, 21, 23] - list all the duplicates - -{{{ continue from paused state }}} - -Duplicates marks are the marks left out when we remove each element of the -list exactly one time. - -:: - - marks = [20, 23, 22, 23, 20, 21, 23] - marks_set = set(marks) - for mark in marks_set: - marks.remove(mark) - - # we are now left with only duplicates in the list marks - duplicates = set(marks) - -{{{ Show summary slide }}} - -This brings us to the end of the tutorial. -we have learnt - - * How to make sets from lists - * How to input sets - * How to perform union, intersection and symmectric difference operations - * How to check if a set is a subset of other - * The various similarities with lists like length and containership - -{{{ Show the "sponsored by FOSSEE" slide }}} - -#[Nishanth]: Will add this line after all of us fix on one. -This tutorial was created as a part of FOSSEE project, NME ICT, MHRD India - -Hope you have enjoyed and found it useful. -Thankyou - -.. Author : Nishanth - Internal Reviewer 1 : - Internal Reviewer 2 : - External Reviewer : - - -Questions -========= - - 1. If ``a = [1, 1, 2, 3, 3, 5, 5, 8]``. What is set(a) - - a. set([1, 1, 2, 3, 3, 5, 5, 8]) - #. set([1, 2, 3, 5, 8]) - #. set([1, 2, 3, 3, 5, 5]) - #. Error - - Answer: set([1, 2, 3, 5, 8]) - - 2. ``a = set([1, 3, 5])``. How do you find the length of a? - - Answer: len(a) - - 3. ``a = set([1, 3, 5])``. What does a[2] produce? - - a. 1 - #. 3 - #. 5 - #. Error - - Answer: Error - - 4. ``odd = set([1, 3, 5, 7, 9])`` and ``squares = set([1, 4, 9, 16])``. What - is the value of ``odd | squares``? - - Answer: set([1, 3, 4, 5, 7, 9, 16]) - - 5. ``odd = set([1, 3, 5, 7, 9])`` and ``squares = set([1, 4, 9, 16])``. What - is the value of ``odd - squares``? - - Answer: set([3, 5, 7]) - - 6. ``odd = set([1, 3, 5, 7, 9])`` and ``squares = set([1, 4, 9, 16])``. What - is the value of ``odd ^ squares``? - - Answer: set([3, 4, 5, 7, 16]) - - 7. ``odd = set([1, 3, 5, 7, 9])`` and ``squares = set([1, 4, 9, 16])``. What - does ``odd * squares`` give? - - a. set([1, 12, 45, 112, 9]) - #. set([1, 3, 4, 5, 7, 9, 16]) - #. set([]) - #. Error - - Answer: Error - - 8. ``a = set([1, 2, 3, 4])`` and ``b = set([5, 6, 7, 8])``. What is ``a + b`` - - a. set([1, 2, 3, 4, 5, 6, 7, 8]) - #. set([6, 8, 10, 12]) - #. set([5, 12, 21, 32]) - #. Error - - 9. ``a`` is a set. how do you check if if a varaible ``b`` exists in ``a``? - - Answer: b in a - - 10. ``a`` and ``b`` are two sets. What is ``a ^ b == (a - b) | (b - a)``? - - a. True - #. False - - Answer: False - - -Problems -======== - - 1. Given that mat_marks is a list of maths marks of a class. Find out the - no.of duplicates marks in the list. - - Answer:: - - unique_marks = set(mat_marks) - no_of_duplicates = len(mat_marks) - len(unique_marks) - - 2. Given that mat_marks is a list of maths marks of a class. Find how many - duplicates of each mark exist. - - Answer:: - - marks_set = set(mat_marks) - for mark in marks_set: - occurences = mat_marks.count(mark) - print occurences - 1, "duplicates of", mark, "exist"