author bhanu
Mon, 15 Nov 2010 15:14:12 +0530
changeset 507 34b8f90a88cb
parent 427 c193744340ba
child 508 a9a87fe550c1
permissions -rw-r--r--
Language check done for `sets`

.. Objectives
.. ----------

.. By the end of this tutorial, you will be able to 

.. * Create sets from lists
.. * Perform union, intersection and symmetric difference operations
.. * Check if a set is a subset of other
.. * understand various similarities with lists like length and containership

.. Prerequisites
.. -------------

..   1. Getting started with lists
.. Author              : Nishanth Amuluru
   Internal Reviewer   : Punch
   External Reviewer   :
   Language Reviewer   : Bhanukiran
   Checklist OK?       : <put date stamp here, if OK> [2010-10-05]


{{{ Show the slide containing title }}}

Hello friends and welcome to the tutorial on Sets

{{{ 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.
    a_list = [1, 2, 1, 4, 5, 6, 2]
    a = set(a_list)
We can see that duplicates are removed and the set contains only unique

    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 | (pipe) character stands for union

    f10 | p10

gives us the union of f10 and p10

The & character stands for intersection.

    f10 & p10

gives the intersection


    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.

    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.


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:

    # 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 symmetric 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 }}}

This tutorial was created as a part of FOSSEE project, NME ICT, MHRD India

Hope you have enjoyed and found it useful.
Thank you!