Removed session 3 -- basic data processing.

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branch : scipyin2010

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diff --git a/day1/session3.tex b/day1/session3.tex
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-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-%Tutorial slides on Python.
-%
-% Author: FOSSEE
-% Copyright (c) 2009, FOSSEE, IIT Bombay
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-
-\documentclass[14pt,compress]{beamer}
-%\documentclass[draft]{beamer}
-%\documentclass[compress,handout]{beamer}
-%\usepackage{pgfpages} 
-%\pgfpagesuselayout{2 on 1}[a4paper,border shrink=5mm]
-
-% Modified from: generic-ornate-15min-45min.de.tex
-\mode<presentation>
-{
-  \usetheme{Warsaw}
-  \useoutertheme{infolines}
-  \setbeamercovered{transparent}
-}
-
-\usepackage[english]{babel}
-\usepackage[latin1]{inputenc}
-%\usepackage{times}
-\usepackage[T1]{fontenc}
-
-% Taken from Fernando's slides.
-\usepackage{ae,aecompl}
-\usepackage{mathpazo,courier,euler}
-\usepackage[scaled=.95]{helvet}
-\usepackage{amsmath}
-
-\definecolor{darkgreen}{rgb}{0,0.5,0}
-
-\usepackage{listings}
-\lstset{language=Python,
-    basicstyle=\ttfamily\bfseries,
-    commentstyle=\color{red}\itshape,
-  stringstyle=\color{darkgreen},
-  showstringspaces=false,
-  keywordstyle=\color{blue}\bfseries}
-
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-% Macros
-\setbeamercolor{emphbar}{bg=blue!20, fg=black}
-\newcommand{\emphbar}[1]
-{\begin{beamercolorbox}[rounded=true]{emphbar} 
-      {#1}
- \end{beamercolorbox}
-}
-\newcounter{time}
-\setcounter{time}{0}
-\newcommand{\inctime}[1]{\addtocounter{time}{#1}{\tiny \thetime\ m}}
-
-\newcommand{\typ}[1]{\lstinline{#1}}
-
-\newcommand{\kwrd}[1]{ \texttt{\textbf{\color{blue}{#1}}}  }
-
-%%% This is from Fernando's setup.
-% \usepackage{color}
-% \definecolor{orange}{cmyk}{0,0.4,0.8,0.2}
-% % Use and configure listings package for nicely formatted code
-% \usepackage{listings}
-% \lstset{
-%    language=Python,
-%    basicstyle=\small\ttfamily,
-%    commentstyle=\ttfamily\color{blue},
-%    stringstyle=\ttfamily\color{orange},
-%    showstringspaces=false,
-%    breaklines=true,
-%    postbreak = \space\dots
-% }
-
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-% Title page
-\title[Statistics]{Python for Science and Engg:\\ Basic data processing}
-
-\author[FOSSEE] {FOSSEE}
-
-\institute[IIT Bombay] {Department of Aerospace Engineering\\IIT Bombay}
-
-\date[] {SciPy 2010, Introductory tutorials,\\Day 1, Session 3}
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-
-%\pgfdeclareimage[height=0.75cm]{iitmlogo}{iitmlogo}
-%\logo{\pgfuseimage{iitmlogo}}
-
-
-%% Delete this, if you do not want the table of contents to pop up at
-%% the beginning of each subsection:
-\AtBeginSubsection[]
-{
-  \begin{frame}<beamer>
-    \frametitle{Outline}
-    \tableofcontents[currentsection,currentsubsection]
-  \end{frame}
-}
-
-\AtBeginSection[]
-{
-  \begin{frame}<beamer>
-    \frametitle{Outline}
-    \tableofcontents[currentsection,currentsubsection]
-  \end{frame}
-}
-
-\newcommand{\num}{\texttt{numpy}}
-
-
-% If you wish to uncover everything in a step-wise fashion, uncomment
-% the following command: 
-%\beamerdefaultoverlayspecification{<+->}
-
-%\includeonlyframes{current,current1,current2,current3,current4,current5,current6}
-
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-% DOCUMENT STARTS
-\begin{document}
-
-\begin{frame}
-  \maketitle
-\end{frame}
-
-%% \begin{frame}
-%%   \frametitle{Outline}
-%%   \tableofcontents
-%%   % You might wish to add the option [pausesections]
-%% \end{frame}
-
-\section{Computing the mean}
-\begin{frame}
-  \frametitle{Value of acceleration due to gravity?}
-  \begin{itemize}
-    \item We already have \typ{pendulum.txt}
-    \item We know that $ T = 2\pi \sqrt{\frac{L}{g}} $
-    \item So $ g = \frac{4 \pi^2 L}{T^2}  $
-    \item Calculate $g$ - acceleration due to gravity for each pair of
-        $L$ and $T$
-    \item Hence calculate mean $g$
-  \end{itemize}
-\end{frame}
-
-\begin{frame}[fragile]
-  \frametitle{Acceleration due to gravity - $g$\ldots}
-  \begin{lstlisting}
-In []: g_list = []
-In []: for line in open('pendulum.txt'):
-  ....     point = line.split()
-  ....     L = float(point[0])
-  ....     t = float(point[1])
-  ....     g = 4 * pi * pi * L / (t * t)
-  ....     g_list.append(g)
-  \end{lstlisting}
-\end{frame}
-
-\begin{frame}[fragile]
-  \frametitle{Mean $g$ - Classical method}
-  \begin{lstlisting}
-In []: total = 0
-In []: for g in g_list:
- ....:     total += g
- ....:
-
-In []: g_mean = total / len(g_list)
-In []: print 'Mean: ', g_mean
-  \end{lstlisting}
-\end{frame}
-
-\begin{frame}[fragile]
-  \frametitle{Mean $g$ - Slightly improved method}
-  \begin{lstlisting}
-In []: g_mean = sum(g_list) / len(g_list)
-In []: print 'Mean: ', g_mean
-  \end{lstlisting}
-\end{frame}
-
-\begin{frame}[fragile]
-  \frametitle{Mean $g$ - One liner}
-  \begin{lstlisting}
-In []: g_mean = mean(g_list)
-In []: print 'Mean: ', g_mean
-  \end{lstlisting}
-  \inctime{10}
-\end{frame}
-
-\section{Processing voluminous data}
-\begin{frame}
-  \frametitle{More on data processing}
-  \begin{block}{}
-    We have a huge data file--180,000 records.\\How do we do
-    \emph{efficient} statistical computations, i.e. find mean, median,
-    standard deviation etc.;\\How do we draw pie charts?
-  \end{block}
-\end{frame}
-
-\begin{frame}
-  \frametitle{Structure of the file}
-  Understanding the structure of \typ{sslc1.txt}
-  \begin{itemize}
-    \item Each line in the file has a student's details(record)
-    \item Each record consists of fields separated by ';'
-  \end{itemize}
-\emphbar{A;015162;JENIL T P;081;060;77;41;74;333;P;;}
-\end{frame}
-
-\begin{frame}
-  \frametitle{Structure of the file \ldots}
-\emphbar{A;015163;JOSEPH RAJ S;083;042;47;AA;72;244;;;}
-  Each record consists of:
-  \begin{itemize}
-    \item Region Code
-    \item Roll Number
-    \item Name
-    \item Marks of 5 subjects: second lang, first lang., Math, Science,
-        Social Studies
-    \item Total marks
-    \item Pass/Fail (P/F)
-    \item Withheld (W)
-  \end{itemize}
-  \inctime{5}
-\end{frame}
-
-\begin{frame}
-  \frametitle{Statistical Analysis: Problem statement}
-  1. Read the data supplied in the file \typ{sslc1.txt} and carry out the following:
-  \begin{itemize}
-    \item[a] Draw a pie chart representing proportion of students who scored more than 90\% in each region in Science.
-    \item[b] Print mean, median and standard deviation of math scores for all regions combined.
-  \end{itemize}
-\end{frame}
-
-\begin{frame}
-  \frametitle{Problem statement: explanation}
-    \emphbar{a. Draw a pie chart representing proportion of students who scored more than 90\% in each region in Science.}
-\begin{columns}
-    \column{5.25\textwidth}
-    \hspace*{.5in}
-\includegraphics[height=2.6in, interpolate=true]{data/science}
-    \column{0.8\textwidth}
-\end{columns}
-\end{frame}
-
-\begin{frame}
-  \frametitle{Machinery Required}
-  \begin{itemize}
-    \item File reading
-    \item Parsing
-    \item Dictionaries 
-    \item Arrays
-    \item Statistical operations
-  \end{itemize}
-\end{frame}
-
-\subsection{Data processing}
-\begin{frame}[fragile]
-  \frametitle{File reading and parsing \ldots}
-\emphbar{Reading files line by line is the same as we had done with the pendulum example.}
-
-  \begin{lstlisting}
-for record in open('sslc1.txt'):
-    fields = record.split(';')
-  \end{lstlisting}
-\end{frame}
-
-\subsection{Dictionaries}
-\begin{frame}[fragile]
-  \frametitle{Dictionaries: Introduction}
-  \begin{itemize}
-    \item Lists index using integers\\
-Recall \typ{p = [2, 3, 5, 7]} and\\
-\typ{p[1]} is equal to \typ{3}
-    \item Dictionaries index using strings
-  \end{itemize}
-\end{frame}
-
-\begin{frame}[fragile]
-  \frametitle{Dictionaries \ldots}
-  \begin{lstlisting}
-In []: d = {'png' : 'image file',
-      'txt' : 'text file', 
-      'py' : 'python code',
-      'java': 'bad code', 
-      'cpp': 'complex code'}
-
-In []: d['txt']
-Out[]: 'text file'
-  \end{lstlisting}
-\end{frame}
-
-\begin{frame}[fragile]
-  \frametitle{Dictionaries \ldots}
-  \begin{lstlisting}
-In []: 'py' in d
-Out[]: True
-
-In []: 'jpg' in d
-Out[]: False
-  \end{lstlisting}
-\end{frame}
-
-\begin{frame}[fragile]
-  \frametitle{Dictionaries \ldots}
-  \begin{small}
-    \begin{lstlisting}
-In []: d.keys()
-Out[]: ['cpp', 'py', 'txt', 'java', 'png']
-
-In []: d.values()
-Out[]: ['complex code', 'python code',
-        'text file', 'bad code', 
-        'image file']
-    \end{lstlisting}
-  \end{small}
-  \inctime{10}
-\end{frame}
-
-\begin{frame}[fragile]
-  \frametitle{Inserting elements into dictionary}
-  \emphbar{\alert{d[key] = value}}
-  \begin{lstlisting}
-    In []: d['bin'] = 'binary file'
-    In []: d
-    Out[]: 
-    {'bin': 'binary file',
-     'cpp': 'complex code',
-     'java': 'bad code',
-     'png': 'image file',
-     'py': 'python code',
-     'txt': 'text file'}
-  \end{lstlisting}
-\end{frame}
-
-\begin{frame}[fragile]
-  \frametitle{Getting back to the problem}
-  Let our dictionary be:
-  \begin{lstlisting}
-science = {}
-  \end{lstlisting}
-\begin{itemize}
-    \item Keys will be region codes
-    \item Values will be the number students who scored more than 90\% in that region in Science
-  \end{itemize}
-  \begin{block}{Sample \typ{science} dictionary}
-    \{'A': 729, 'C': 764, 'B': 1120,'E': 414, 'D': 603, 'F': 500\}
-  \end{block}
-
-\end{frame}
-
-\begin{frame}[fragile]
-  \frametitle{Building parsed data \ldots}
-  \begin{lstlisting}
-science = {}
-
-for record in open('sslc1.txt'):
-    fields = record.split(';')
-
-    region_code = fields[0].strip()
-  \end{lstlisting}
-\end{frame}
-
-\begin{frame}[fragile]
-  \frametitle{Building parsed data \ldots}
-  \begin{lstlisting}
-    if region_code not in science:
-        science[region_code] = 0
-
-    score_str = fields[6].strip()
-
-    score = 0
-    if score_str != 'AA':
-        score = int(score_str)
-
-    if score > 90:
-        science[region_code] += 1
-  \end{lstlisting}
-\end{frame}
-
-\begin{frame}[fragile]
-  \frametitle{Building parsed data \ldots}
-  \begin{lstlisting}
-print science
-print science.keys()
-print science.values()
-  \end{lstlisting}
-\end{frame}
-
-\subsection{Visualizing data}
-\begin{frame}[fragile]
-  \frametitle{Pie Chart}
-  \begin{lstlisting}
-    pie(science.values())
-  \end{lstlisting}
-\includegraphics[height=2in, interpolate=true]{data/science_nolabel}
-\end{frame}
-
-\begin{frame}[fragile]
-  \frametitle{Pie chart}
-  \small
-  \begin{lstlisting}
-pie(science.values(), 
-    labels = science.keys())
-title('Students scoring 90% and above 
-      in science by region')
-savefig('science.png')
-  \end{lstlisting}
-\begin{columns}
-    \column{5.25\textwidth}
-    \hspace*{1.1in}
-\includegraphics[height=2in, interpolate=true]{data/science}
-    \column{0.8\textwidth}
-\end{columns}
-  \inctime{10}
-\end{frame}
-
-\begin{frame}
-  \frametitle{Problem statement}
-    \emphbar{b. Print mean, median and standard deviation of math scores for all regions combined.}
-\end{frame}
-
-\begin{frame}[fragile]
-  \frametitle{Building data for statistics}
-  \begin{lstlisting}
-math_scores = []
-
-for record in open('sslc1.txt'):
-    fields = record.split(';')
-
-    score_str = fields[5].strip()
-    score = 0
-    if score_str != 'AA':
-        score = int(score_str)
-
-    math_scores.append(score)
-  \end{lstlisting}
-\end{frame}
-
-\subsection{Obtaining statistics}
-\begin{frame}[fragile]
-  \frametitle{Obtaining statistics}
-  \begin{lstlisting}
-print 'Mean: ', mean(math_scores)
-
-print 'Median: ', median(math_scores)
-
-print 'Standard Deviation: ',
-              std(math_scores)
-  \end{lstlisting}
-  \inctime{10}
-\end{frame}
-
-\begin{frame}[fragile]
-  \frametitle{Obtaining statistics: efficiently!}
-  \begin{lstlisting}
-math_array = array(math_scores)
-
-print 'Mean: ', mean(math_array)
-
-print 'Median: ', median(math_array)
-
-print 'Standard Deviation: ',
-              std(math_array)
-  \end{lstlisting}
-  \inctime{5}
-\end{frame}
-
-\begin{frame}[fragile]
-  \frametitle{IPython tip: Timing}
-
-Try the following:
-  \begin{lstlisting}
-In []: %timeit mean(math_scores)
-
-In []: %timeit mean(math_array)
-
-In []: %timeit?
-
-  \end{lstlisting}
-
-  \begin{itemize}
-      \item \typ{\%timeit}: accurate, many measurements
-      \item Can also use \typ{\%time}
-      \item \typ{\%time}: less accurate, one measurement 
-  \end{itemize}
-
-  \inctime{5}
-\end{frame}
-
-\begin{frame}[fragile]
-  \frametitle{What tools did we use?}
-  \begin{itemize}
-   \item More parsing data
-   \item Dictionaries for storing data
-   \item Facilities for drawing pie charts
-   \item Functions for statistical computations - mean, median, standard deviation
-   \item Efficient array manipulations
-   \item Timing in IPython
-  \end{itemize}
-
-\end{frame}
-
-\end{document}
-
-%% Questions for Quiz %%
-%% ------------------ %%
-
-\begin{frame}
-\frametitle{\incqno }
-  A sample line from a Comma Separated Values (CSV) file:\\
-  \vspace*{0.2in}
-  \emph{Rossum, Guido, 42, 56, 34, 54}\\
-  \vspace*{0.2in}
-  What code would you use to separate the line into fields?
-\end{frame}
-
-\begin{frame}[fragile]
-\frametitle{\incqno }
-  \begin{lstlisting}
-  In []: a = [1, 2, 5, 9]
-  \end{lstlisting}
-  How do you find the length of this list?
-\end{frame}
-
-\begin{frame}[fragile]
-\frametitle{\incqno }
-  \begin{lstlisting}
-  In [1]: d = {
-          'a': 1,
-          'b': 2
-          }
-  In [2]: print d['c']
-  \end{lstlisting}
-  What is the output?
-\end{frame}
-
-\begin{frame}[fragile]
-\frametitle{\incqno }
-\begin{lstlisting}
-In []: sc = {'A': 10, 'B': 20, 
-             'C': 70}
-\end{lstlisting}
-Given the above dictionary, what command will you give to plot a
-pie-chart?
-\end{frame}
-
-\begin{frame}[fragile]
-\frametitle{\incqno }
-\begin{lstlisting}
-In []: marks = [10, 20, 30, 50, 55, 
-                75, 83] 
-\end{lstlisting}
-Given the above marks, how will you calculate the \alert{mean} and
-\alert{standard deviation}?
-\end{frame}
-
-\begin{frame}[fragile]
-\frametitle{\incqno }
-\begin{lstlisting}
-In []: marks = [10, 20, 30, 50, 55, 
-               75, 83] 
-\end{lstlisting}
-How will you convert the list \texttt{marks} to an \alert{array}?
-\end{frame}
-
-%% \begin{frame}[fragile]
-%% \frametitle{\incqno }
-%%   \begin{lstlisting}
-%%   for x in "abcd":
-%%       print x
-
-%%   a
-%%   b
-%%   c
-%%   d
-%%   \end{lstlisting}
-%%   How do you get the following output? 
-%%   \begin{lstlisting}
-%%     0 a
-%%     1 b
-%%     2 c
-%%     3 d
-%%   \end{lstlisting}
-%% \end{frame}
-