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sets/script.rst

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] Script ------ {{{ 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. type :: a_list = [1, 2, 1, 4, 5, 6, 2] 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 | (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 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 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!