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  {
   "cells": [
    {
     "cell_type": "heading",
     "level": 1,
     "metadata": {},
     "source": [
      "Hands-on: Python Fundamentals -- Sets"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "**Objectives:**\n",
      "\n",
      "Upon completion of this lesson, you should be able to:\n",
      "\n",
      "* Describe the characteristics of the builtin `set` container in Python\n",
      "\n",
      "* Perform basic operations with `set`s including creation, \"querying\", updates, and basic set operations\n",
      "\n",
      "* Get an idea in which situations `set`s are and should be used"
     ]
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "The set data structure"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "* In Python, a `set` is an efficient storage for \"membership\" checking\n",
      "\n",
      "* **`set` is like a `dict` but only with keys and without values**"
     ]
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "The set data structure"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "* Values are similar to \"keys\" in `dict` and can be any Python data type **BUT**\n",
      "\n",
      "* they **should be immutable**"
     ]
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "Creating a set"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "* There are a number of ways to create and fill a set.  E.g. you can create an empty one and keep assining new values"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# Create an empty set\n",
      "eng = set()\n",
      "print eng"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "eng.add('one')\n",
      "print eng"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "eng.add('two')\n",
      "print eng"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "heading",
     "level": 3,
     "metadata": {},
     "source": [
      "Creating a set \"hardcoded\" way"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "* Very similar to `dict` but without values.  As well as with `dict`, the order of items in a set is unpredictable"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "eng = {'one', 'two', 'three'}\n",
      "print eng"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "heading",
     "level": 3,
     "metadata": {},
     "source": [
      "Creating a set from a list"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "You can create a set from an iterable (e.g. list):"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "eng = set(['one', 'two', 'three'])\n",
      "print eng"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "heading",
     "level": 3,
     "metadata": {},
     "source": [
      "Set comprehension"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Very similar to dict comprehensions:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "{e for e in ['one', 'two', 'three'] if 'e' in e}"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "The in operator"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "Very similar to lists and tuples:"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "6 in {4, 5, 6, 7}\n",
      "True"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "Deleting items"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "eng.add('five')\n",
      "print eng\n",
      "eng.remove('five')\n",
      "print eng"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "heading",
     "level": 2,
     "metadata": {},
     "source": [
      "Why the heck \"set\"s?"
     ]
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "**Why do we need sets if we could check for membership in lists and tuples?**\n"
     ]
    },
    {
     "cell_type": "heading",
     "level": 3,
     "metadata": {},
     "source": [
      "1. Because lookup in a `set` is much faster"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "def lookups(container):\n",
      "    for i in range(100, 200):\n",
      "        i in container"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "import random\n",
      "l = range(1000)\n",
      "random.shuffle(l)\n",
      "t = tuple(l)\n",
      "s = set(l)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%timeit lookups(l)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%timeit lookups(t)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "%timeit lookups(s)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "heading",
     "level": 3,
     "metadata": {},
     "source": [
      "2. Because they provide set operations"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "print dir(set)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "{1, 2, 3, 'mom', 'dad'}.union({2, 3, 10})"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "{1, 2, 3, 'mom', 'dad'} | {2, 3, 10}"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "{1, 2, 3, 'mom', 'dad'}.intersection({2, 3, 10})"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "{1, 2, 3, 'mom', 'dad'} & {2, 3, 10}"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "{1, 2, 3, 'mom', 'dad'}.difference({2, 3, 10})"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "{1, 2, 3, 'mom', 'dad'} - {2, 3, 10}"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "More on sets could be found in the documentation: https://docs.python.org/2/library/stdtypes.html#set"
     ]
    }
   ],
   "metadata": {}
  }
 ]
}