% Created 2010-11-03 Wed 15:37
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\title{Accessing parts of arrays}
\author{FOSSEE}
\date{}

\begin{document}

\maketitle









\begin{frame}
\frametitle{Outline}
\label{sec-1}

\begin{itemize}
\item Manipulating one and multi dimensional arrays
\item Access and change individual elements
\item Access and change rows and columns
\item Slicing and striding on arrays to access chunks
\item Read images into arrays and manipulations
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Sample Arrays}
\label{sec-2}

\begin{verbatim}
In []: A = array([12, 23, 34, 45, 56])

In []: C = array([[11, 12, 13, 14, 15],
                  [21, 22, 23, 24, 25],
                  [31, 32, 33, 34, 35],
                  [41, 42, 43, 44, 45],
                  [51, 52, 53, 54, 55]])
\end{verbatim}
\end{frame}
\begin{frame}
\frametitle{Question 1}
\label{sec-3}

  Change the last column of \texttt{C} to zeroes. 
\end{frame}
\begin{frame}[fragile]
\frametitle{Solution 1}
\label{sec-4}

\begin{verbatim}
In []:  C[:, -1] = 0
\end{verbatim}
\end{frame}
\begin{frame}
\frametitle{Question 2}
\label{sec-5}

  Change \texttt{A} to \texttt{[11, 12, 13, 14, 15]}. 
\end{frame}
\begin{frame}[fragile]
\frametitle{Solution 2}
\label{sec-6}

\begin{verbatim}
In []:  A[:] = [11, 12, 13, 14, 15]
\end{verbatim}
\end{frame}
\begin{frame}
\frametitle{squares.png}
\label{sec-7}

    \begin{center}
      \includegraphics[scale=0.6]{squares}    
    \end{center}
\end{frame}
\begin{frame}
\frametitle{Question 3}
\label{sec-8}

\begin{itemize}
\item obtain \texttt{[22, 23]} from \texttt{C}.
\item obtain \texttt{[11, 21, 31, 41]} from \texttt{C}.
\item obtain \texttt{[21, 31, 41, 0]}.
\end{itemize}
\end{frame}
\begin{frame}[fragile]
\frametitle{Solution 3}
\label{sec-9}

\begin{verbatim}
In []:  C[1, 1:3]
In []:  C[0:4, 0]
In []:  C[1:5, 0]
\end{verbatim}
\end{frame}
\begin{frame}
\frametitle{Question 4}
\label{sec-10}

  Obtain \texttt{[[23, 24], [33, -34]]} from \texttt{C}
\end{frame}
\begin{frame}[fragile]
\frametitle{Solution 4}
\label{sec-11}

\begin{verbatim}
In []:  C[1:3, 2:4]
\end{verbatim}
\end{frame}
\begin{frame}
\frametitle{Question 5}
\label{sec-12}

  Obtain the square in the center of the image
\end{frame}
\begin{frame}[fragile]
\frametitle{Solution 5}
\label{sec-13}

\begin{verbatim}
In []: imshow(I[75:225, 75:225])
\end{verbatim}
\end{frame}
\begin{frame}[fragile]
\frametitle{Question 6}
\label{sec-14}

  Obtain the following
\begin{verbatim}
[[12, 0], [42, 0]]
[[12, 13, 14], [0, 0, 0]]
\end{verbatim}
\end{frame}
\begin{frame}[fragile]
\frametitle{Solution 6}
\label{sec-15}

\begin{verbatim}
In []: C[::3, 1::3]
In []: C[::4, 1:4]
\end{verbatim}
\end{frame}
\begin{frame}
\frametitle{Summary}
\label{sec-16}

  You should now be able to --
\begin{itemize}
\item Manipulate single \& multi dimensional arrays

\begin{itemize}
\item Access and change individual elements
\item Access and change rows and columns
\item Slice and stride on arrays
\end{itemize}

\item Read images into arrays and manipulate them.
\end{itemize}
\end{frame}
\begin{frame}
\frametitle{Thank you!}
\label{sec-17}

  \begin{block}{}
  \begin{center}
  This spoken tutorial has been produced by the
  \textcolor{blue}{FOSSEE} team, which is funded by the 
  \end{center}
  \begin{center}
    \textcolor{blue}{National Mission on Education through \\
      Information \& Communication Technology \\ 
      MHRD, Govt. of India}.
  \end{center}  
  \end{block}
\end{frame}

\end{document}