{
 "metadata": {
  "gist_id": "Error: No such file or directory - usrlocalnotebooksNo",
  "name": ""
 },
 "nbformat": 3,
 "nbformat_minor": 0,
 "worksheets": [
  {
   "cells": [
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "# Lists\n",
      "\n",
      "* Put objects into a container;\n",
      "* labelled by position;\n",
      "* retrieve them by position, OR iterate over them."
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "some_list = []\n",
      "some_list.append(5)\n",
      "some_list.append(6)\n",
      "some_list.append(7)\n",
      "\n",
      "print some_list\n",
      "for item in some_list:\n",
      "    print item"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "[5, 6, 7]\n",
        "5\n",
        "6\n",
        "7\n"
       ]
      }
     ],
     "prompt_number": 14
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "### HW 3.1"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# Write Python code to calculate the average of the numbers in some_list; it should work for any set of numbers in some_list.\n",
      "print (5 + 6 + 7)/3.\n",
      "\n",
      "some_list=[1,2]\n",
      "\n",
      "print some_list\n",
      "\n",
      "total = 0.0\n",
      "for item in some_list:\n",
      "    total = total + item\n",
      "    \n",
      "average = total / len(some_list)\n",
      "print average\n",
      "\n",
      "print float(sum(some_list))/len(some_list)\n",
      "\n",
      "import numpy\n",
      "print numpy.mean(some_list)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "6.0\n",
        "[1, 2]\n",
        "1.5\n",
        "1.5\n",
        "1.5\n"
       ]
      }
     ],
     "prompt_number": 29
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "# Dictionaries\n",
      "\n",
      "* put things into a container, labeled with a name;\n",
      "* retrieve them;\n",
      "* iterate over labels/names"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# for example, combining lists [] and dicts {} can be useful:\n",
      "letters_list = ['a', 'b', 'c', 'd', 'e']\n",
      "\n",
      "letters_dict = {}\n",
      "\n",
      "for i in range(len(letters_list)):\n",
      "    single_letter = letters_list[i]\n",
      "    letters_dict[single_letter] = i"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "### HW 3.2"
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "some_list = [\"duck\", \"goose\", \"mouse\", \"mouse\", \"mouse\", \"duck\"]\n",
      "\n",
      "counts = {}\n",
      "counts[\"duck\"] = 0\n",
      "\n",
      "for item in some_list:\n",
      "    if item == \"duck\":\n",
      "        counts[\"duck\"] += 1"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 31
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "## Write Python code to generically count the number of times *each* item in some_list is there.\n",
      "## The output should be in dictionary format, e.g. 'print counts[\"duck\"]' should show '2'.\n",
      "n_ducks = 0\n",
      "n_mice=0\n",
      "n_geese=0\n",
      "\n",
      "for item in some_list:\n",
      "    if item == \"duck\":\n",
      "        n_ducks += 1\n",
      "\n",
      "### ^^^ that's how you'd do it if you weren't using dictionaries\n",
      "\n",
      "counts = {}\n",
      "for item in some_list:\n",
      "    counts[item] = 0\n",
      "    \n",
      "for item in some_list:\n",
      "    counts[item] = counts[item] + 1\n",
      "    \n",
      "print counts"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "{'goose': 1, 'mouse': 3, 'duck': 2}\n"
       ]
      }
     ],
     "prompt_number": 39
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# identical to ^^^\n",
      "counts = {}\n",
      "for item in some_list:\n",
      "    counts[item] = counts.get(item, 0) + 1\n",
      "    \n",
      "print counts"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "{'goose': 1, 'mouse': 3, 'duck': 2}\n"
       ]
      }
     ],
     "prompt_number": 38
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "counts = {}\n",
      "for item in some_list:\n",
      "    n = 0\n",
      "    for item2 in some_list:\n",
      "        if item == item2:\n",
      "            n += 1\n",
      "    counts[item] = n\n",
      "    # equivalent to\n",
      "    #counts[item] = some_list.count(item)\n",
      "print counts"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "{'goose': 1, 'mouse': 3, 'duck': 2}\n"
       ]
      }
     ],
     "prompt_number": 41
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "s = \"ATGGACCAGATGGACACAGATTAGAGAGA\"\n",
      "\n",
      "counts = {}\n",
      "for ch in s:\n",
      "    print 'at', ch, 'counts is', counts.get(ch, 0)\n",
      "    counts[ch] = counts.get(ch, 0) + 1\n",
      "print counts\n",
      "\n",
      "counts2 = {}\n",
      "K = 4\n",
      "for i in range(len(s) - K + 1):\n",
      "    word = s[i:i+K]\n",
      "    counts2[word] = counts2.get(word, 0) + 1\n",
      "print counts2"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "at A counts is 0\n",
        "at T counts is 0\n",
        "at G counts is 0\n",
        "at G counts is 1\n",
        "at A counts is 1\n",
        "at C counts is 0\n",
        "at C counts is 1\n",
        "at A counts is 2\n",
        "at G counts is 2\n",
        "at A counts is 3\n",
        "at T counts is 1\n",
        "at G counts is 3\n",
        "at G counts is 4\n",
        "at A counts is 4\n",
        "at C counts is 2\n",
        "at A counts is 5\n",
        "at C counts is 3\n",
        "at A counts is 6\n",
        "at G counts is 5\n",
        "at A counts is 7\n",
        "at T counts is 2\n",
        "at T counts is 3\n",
        "at A counts is 8\n",
        "at G counts is 6\n",
        "at A counts is 9\n",
        "at G counts is 7\n",
        "at A counts is 10\n",
        "at G counts is 8\n",
        "at A counts is 11\n",
        "{'A': 12, 'C': 4, 'T': 4, 'G': 9}\n",
        "{'ACAG': 1, 'GGAC': 2, 'ACAC': 1, 'ATGG': 2, 'TTAG': 1, 'TGGA': 2, 'GATT': 1, 'GAGA': 2, 'ACCA': 1, 'GACA': 1, 'CACA': 1, 'TAGA': 1, 'ATTA': 1, 'AGAT': 2, 'CAGA': 2, 'AGAG': 2, 'GACC': 1, 'GATG': 1, 'CCAG': 1}\n"
       ]
      }
     ],
     "prompt_number": 37
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "# Functions\n",
      "\n",
      "Functions encapsulate code to make it reusable by making it generic and labelling it."
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "def add_two_numbers(a, b):\n",
      "    c = a + b\n",
      "    return c\n",
      "\n",
      "add_two_numbers(5, 10)"
     ],
     "language": "python",
     "metadata": {},
     "outputs": []
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "### HW 3.3\n",
      "\n",
      "Write functions for one or both of the above exercises; e.g."
     ]
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "# make the below code work by defining a new function, 'average'\n",
      "\n",
      "def average(the_list):\n",
      "    total = 0.0\n",
      "    for item in the_list:\n",
      "        total = total + item\n",
      "    \n",
      "    result = total / len(the_list)\n",
      "    return result"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 56
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "some_list = []\n",
      "some_list.append(5)\n",
      "some_list.append(6)\n",
      "some_list.append(7)\n",
      "print average(some_list)\n",
      "\n",
      "some_list"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "8.25\n"
       ]
      },
      {
       "metadata": {},
       "output_type": "pyout",
       "prompt_number": 55,
       "text": [
        "[5, 6, 7, 15]"
       ]
      }
     ],
     "prompt_number": 55
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "def count_items(the_list):\n",
      "    counts = {}\n",
      "    for item in some_list:\n",
      "        counts[item] = 0\n",
      "    \n",
      "    for item in some_list:\n",
      "        counts[item] = counts[item] + 1\n",
      "    return counts"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [],
     "prompt_number": 57
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": [
      "some_list = [\"duck\", \"goose\", \"mouse\", \"mouse\", \"mouse\", \"duck\"]\n",
      "\n",
      "counts_dict = count_items(some_list)\n",
      "print counts_dict\n",
      "print \"duck shows up\", counts_dict[\"duck\"], \"times\""
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "{'goose': 1, 'mouse': 3, 'duck': 2}\n",
        "duck shows up 2 times\n"
       ]
      }
     ],
     "prompt_number": 59
    },
    {
     "cell_type": "markdown",
     "metadata": {},
     "source": [
      "## Upload your homework\n",
      "\n",
      "When you're done, save the file and run the following cell.  It will give you a URL like 'https://gist.github.com/7036805'.  Take the number at the end and go to 'http://nbviewer.ipython.org' and enter it into the box; hit enter.  You should see a static version of your notebook.  Send me that URL as part of your homework hand-in (e.g. http://nbviewer.ipython.org/7036805)."
     ]
    },
    {
     "cell_type": "code",
     "collapsed": true,
     "input": [
      "!gist class3-lists-dicts-functions.ipynb"
     ],
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "https://gist.github.com/7036800\r\n"
       ]
      }
     ],
     "prompt_number": 4
    }
   ],
   "metadata": {}
  }
 ]
}