ngs-61-intro-to-dicts.ipynb

{
 "metadata": {
  "name": "ngs-61-intro-to-dicts"
 },
 "nbformat": 3,
 "worksheets": [
  {
   "cells": [
    {
     "cell_type": "markdown",
     "source": [
      "Goal: take some data from counting birds, and ask questions of it.",
      "",
      "In particular, how many birds did we see of each type?"
     ]
    },
    {
     "cell_type": "code",
     "input": [
      "s = \"\"\"",
      "bluejay",
      "goldfinch",
      "goldfinch",
      "bald eagle",
      "ostrich",
      "bluejay",
      "goose",
      "goose",
      "goose",
      "goose",
      "goose",
      "goose",
      "goose",
      "duck",
      "\"\"\""
     ],
     "language": "python",
     "outputs": [],
     "prompt_number": 1
    },
    {
     "cell_type": "markdown",
     "source": [
      "First, let's transform this text list into a \"real\" python list."
     ]
    },
    {
     "cell_type": "code",
     "input": [
      "birdlist = s.split('\\n')",
      "birdlist = [ x for x in birdlist if x ]",
      "birdlist"
     ],
     "language": "python",
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 6,
       "text": [
        "['bluejay',",
        " 'goldfinch',",
        " 'goldfinch',",
        " 'bald eagle',",
        " 'ostrich',",
        " 'bluejay',",
        " 'goose',",
        " 'goose',",
        " 'goose',",
        " 'goose',",
        " 'goose',",
        " 'goose',",
        " 'goose',",
        " 'duck']"
       ]
      }
     ],
     "prompt_number": 6
    },
    {
     "cell_type": "code",
     "input": [
      "countlist = []",
      "for bird in birdlist:",
      "    newcountlist = []",
      "    found = False",
      "    for (j, count) in countlist:",
      "        if j == bird:",
      "            found = True",
      "            count += 1",
      "        newcountlist.append((j, count))",
      "    if not found:",
      "        newcountlist.append((bird, 1))",
      "    countlist = newcountlist",
      "    ",
      "countlist"
     ],
     "language": "python",
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 9,
       "text": [
        "[('bluejay', 2),",
        " ('goldfinch', 2),",
        " ('bald eagle', 1),",
        " ('ostrich', 1),",
        " ('goose', 7),",
        " ('duck', 1)]"
       ]
      }
     ],
     "prompt_number": 9
    },
    {
     "cell_type": "markdown",
     "source": [
      "Let's use a dictionary instead"
     ]
    },
    {
     "cell_type": "code",
     "input": [
      "birddict = {}",
      "# set the value associated with the key 'goose' to the number 7",
      "birddict['goose'] = 7",
      "# get the value associated with the key 'goose'",
      "print birddict['goose']"
     ],
     "language": "python",
     "outputs": [
      {
       "output_type": "stream",
       "stream": "stdout",
       "text": [
        "7",
        ""
       ]
      }
     ],
     "prompt_number": 10
    },
    {
     "cell_type": "code",
     "input": [
      "birddict = {}",
      "for bird in birdlist:",
      "    birddict[bird] = 0",
      "    ",
      "for bird in birdlist:",
      "    birddict[bird] = birddict[bird] + 1",
      "",
      "birddict"
     ],
     "language": "python",
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 14,
       "text": [
        "{'bald eagle': 1,",
        " 'bluejay': 2,",
        " 'duck': 1,",
        " 'goldfinch': 2,",
        " 'goose': 7,",
        " 'ostrich': 1}"
       ]
      }
     ],
     "prompt_number": 14
    },
    {
     "cell_type": "code",
     "input": [
      "birddict = {}",
      "",
      "for bird in birdlist:",
      "    if bird not in birddict:",
      "        birddict[bird] = 1",
      "    else:",
      "        birddict[bird] = birddict[bird] + 1",
      "",
      "birddict"
     ],
     "language": "python",
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 17,
       "text": [
        "{'bald eagle': 1,",
        " 'bluejay': 2,",
        " 'duck': 1,",
        " 'goldfinch': 2,",
        " 'goose': 7,",
        " 'ostrich': 1}"
       ]
      }
     ],
     "prompt_number": 17
    },
    {
     "cell_type": "code",
     "input": [
      "birddict = {}",
      "",
      "for bird in birdlist:",
      "    birddict[bird] = birddict.get(bird, 0) + 1",
      "",
      "birddict"
     ],
     "language": "python",
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 18,
       "text": [
        "{'bald eagle': 1,",
        " 'bluejay': 2,",
        " 'duck': 1,",
        " 'goldfinch': 2,",
        " 'goose': 7,",
        " 'ostrich': 1}"
       ]
      }
     ],
     "prompt_number": 18
    },
    {
     "cell_type": "code",
     "input": [
      "birddict.keys()"
     ],
     "language": "python",
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 19,
       "text": [
        "['bald eagle', 'bluejay', 'ostrich', 'goose', 'goldfinch', 'duck']"
       ]
      }
     ],
     "prompt_number": 19
    },
    {
     "cell_type": "code",
     "input": [
      "birddict.values()"
     ],
     "language": "python",
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 20,
       "text": [
        "[1, 2, 1, 7, 2, 1]"
       ]
      }
     ],
     "prompt_number": 20
    },
    {
     "cell_type": "code",
     "input": [
      "birddict.items()"
     ],
     "language": "python",
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 21,
       "text": [
        "[('bald eagle', 1),",
        " ('bluejay', 2),",
        " ('ostrich', 1),",
        " ('goose', 7),",
        " ('goldfinch', 2),",
        " ('duck', 1)]"
       ]
      }
     ],
     "prompt_number": 21
    },
    {
     "cell_type": "code",
     "input": [
      "x = sorted(birddict.items())",
      "x"
     ],
     "language": "python",
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 23,
       "text": [
        "[('bald eagle', 1),",
        " ('bluejay', 2),",
        " ('duck', 1),",
        " ('goldfinch', 2),",
        " ('goose', 7),",
        " ('ostrich', 1)]"
       ]
      }
     ],
     "prompt_number": 23
    },
    {
     "cell_type": "code",
     "input": [
      "def get_count(a):",
      "    return a[1]",
      "",
      "# Sort by count, not by bird name; use get_count to get the count.",
      "x = sorted(birddict.items(), key=get_count)",
      "# by default sorted goes from least to most; reverse that.",
      "x.reverse()",
      "x"
     ],
     "language": "python",
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 33,
       "text": [
        "[('goose', 7),",
        " ('goldfinch', 2),",
        " ('bluejay', 2),",
        " ('duck', 1),",
        " ('ostrich', 1),",
        " ('bald eagle', 1)]"
       ]
      }
     ],
     "prompt_number": 33
    },
    {
     "cell_type": "code",
     "input": [
      ""
     ],
     "language": "python",
     "outputs": []
    },
    {
     "cell_type": "code",
     "input": [
      ""
     ],
     "language": "python",
     "outputs": []
    }
   ]
  }
 ]
}