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%Tutorial slides on Python.

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% Author: FOSSEE

% Copyright (c) 2009, FOSSEE, IIT Bombay

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% Title page

\title[Statistics]{Python for Science and Engg: Statistics}

\author[FOSSEE] {FOSSEE}

\institute[IIT Bombay] {Department of Aerospace Engineering\\IIT Bombay}

\date[] {7 November, 2009\\Day 1, Session 3}

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%% the beginning of each subsection:

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    \frametitle{Outline}

    \tableofcontents[currentsection,currentsubsection]

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    \frametitle{Outline}

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% 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 mean}

\begin{frame}

  \frametitle{Value of acceleration due to gravity?}

  \begin{itemize}

    \item We already have 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 = []

In []: for line in open('pendulum.txt'):

  ....     points = line.split()

  ....     l = float(points[0])

  ....     t = float(points[1])

  ....     g = 4 * pi * pi * l / t * t

  ....     G.append(g)

  \end{lstlisting}

\end{frame}

\begin{frame}

  \frametitle{Computing mean ``g''}

  \begin{block}{Exercise}

    Obtain the mean of ``g''

  \end{block}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Mean ``g''}

  \begin{lstlisting}

total = 0

for g in G:

    total += g

mean_g = total / len(g)

print "Mean: ", mean_g

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Mean ``g''}

  \begin{lstlisting}

mean_g = sum(G) / len(G)

print "Mean: ", mean_g

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Mean ``g''}

  \begin{lstlisting}

mean_g = mean(G)

print "Mean: ", mean_g

  \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; draw pie charts?

  \end{block}

\end{frame}

\begin{frame}

  \frametitle{Structure of the file}

  Understanding the structure of 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: English, Hindi, Maths, Science, Social

    \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 \emph{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 List enumeration

    \item Arrays

    \item Statistical operations

  \end{itemize}

\end{frame}

\subsection{Data processing}

\begin{frame}[fragile]

  \frametitle{File reading and parsing \ldots}

  \begin{lstlisting}

for record in open('sslc1.txt'):

    fields = record.split(';')

  \end{lstlisting}

\begin{block}{}

\centerline{Recall pendulum example!}

\end{block}

\end{frame}

\subsection{Dictionaries}

\begin{frame}[fragile]

  \frametitle{Dictionaries: Introduction}

  \begin{itemize}

    \item lists index: 0 \ldots n

    \item dictionaries index using strings

  \end{itemize}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Dictionaries \ldots}

  \begin{lstlisting}

In []: d = {"jpg" : "image file",

      "txt" : "text file", 

      "py" : "python 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 []: "cpp" in d

Out[]: False

  \end{lstlisting}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Dictionaries \ldots}

  \begin{lstlisting}

In []: d.keys()

Out[]: ['py', 'txt', 'jpg']

In []: d.values()

Out[]: ['python code', 'text file',

       'image file']

  \end{lstlisting}

  \inctime{10}

\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

  \end{itemize}

\end{frame}

\begin{frame}[fragile]

  \frametitle{Building parsed data \ldots}

  \begin{lstlisting}

science = {}

for record in open('sslc1.txt'):

    record = record.strip()

    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 = int(score_str) if \

    score_str != 'AA' else 0

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}

  \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'):

    record = record.strip()

    fields = record.split(';')

    score_str = fields[5].strip()

    score = int(score_str) if \

      score_str != 'AA' else 0

    math_scores.append(score)

  \end{lstlisting}

\end{frame}

\subsection{Obtaining statistics}

\begin{frame}[fragile]

  \frametitle{Obtaining statistics}

  \begin{block}{Exercise}

    Obtain the mean of Math scores

  \end{block}

\end{frame}

\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{What tools did we use?}

  \begin{itemize}

   \item Dictionaries for storing data

   \item Facilities for drawing pie charts

   \item Efficient array manipulations

   \item Functions for statistical computations - mean, median, standard deviation

  \end{itemize}

\end{frame}

\end{document}