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    20 

    21 #+TITLE: Getting started with arrays

    22 #+AUTHOR: FOSSEE

    23 #+EMAIL: info@fossee.in

    24 #+DATE:    

    25 

    26 #+DESCRIPTION: 

    27 #+KEYWORDS: 

    28 #+LANGUAGE:  en

    29 #+OPTIONS:   H:3 num:nil toc:nil \n:nil @:t ::t |:t ^:t -:t f:t *:t <:t

    30 #+OPTIONS:   TeX:t LaTeX:nil skip:nil d:nil todo:nil pri:nil tags:not-in-toc

    31 

    32 * Outline

    33   - Arrays

    34     - why arrays over lists

    35   - Creating arrays

    36   - Array operations

    37 

    38 * Overview of Arrays

    39   - Arrays are homogeneous data structures.

    40     - elements have to the same data type

    41   - Arrays are faster compared to lists

    42     - at least /80-100 times/ faster than lists

    43 

    44 * Creating Arrays

    45   - Creating a 1-dimensional array

    46   : In []: a1 = array([1, 2, 3, 4])

    47   ~[1, 2, 3, 4]~ is a list.

    48 * Creating two-dimensional array

    49   - Creating a 2-dimensional array

    50   : In []: a2 = array([[1,2,3,4],[5,6,7,8]])

    51   here we convert a list of lists to an array making a 2-d array.

    52   - Using ~arange()~ function

    53   : In []: ar = arange(1,9)

    54 * ~reshape()~ method

    55   - To reshape an array

    56   : In []: ar.reshape(2, 4)

    57   : In []: ar.reshape(4, 2)

    58   : In []: ar = ar.reshape(2, 4)

    59 

    60 * Creating ~array~ from ~list~.

    61   - ~array()~ method accepts list as argument

    62   - Creating a list

    63    : In []: l1 = [1, 2, 3, 4]

    64   - Creating an array

    65     : In []: a3 = array(l1)

    66 

    67 * Exercise 1

    68   Create a 3-dimensional array of the order (2, 2, 4).

    69 

    70 * ~.shape~ of array

    71   - ~.shape~

    72     To find the shape of the array

    73     : In []: a2.shape

    74   - ~.shape~

    75     returns a tuple of shape

    76 * Exercise 2

    77   Find out the shape of the other arrays(a1, a3, ar) that we have created.

    78 * Homogeneous data

    79   - All elements in array should be of same type

    80     : In []: a4 = array([1,2,3,'a string'])

    81 * Implicit type casting 

    82    : In []: a4

    83     All elements are type casted to string type

    84 * ~identity()~, ~zeros()~ methods

    85   - ~identity(n)~

    86     Creates an identity matrix, a square matrix of order (n, n) with diagonal elements 1 and others 0.

    87   - ~zeros((m, n))~

    88     Creates an ~m X n~ matrix with all elements 0.

    89 

    90 * Learning exercise

    91   - Find out about

    92     - ~zeros_like()~

    93     - ~ones()~

    94     - ~ones_like()~

    95 

    96 * Array operations

    97   - ~a1 * 2~

    98     returns a new array with all elements of ~a1~ multiplied by ~2~.

    99     - Similarly ~+~, ~-~ \& ~/~.

   100   - ~a1 + 2~

   101     returns a new array with all elements of ~a1~ summed with ~2~.

   102   - ~a1 += 2~

   103     adds ~2~ to all elements of array ~a1~.

   104     - Similarly ~-=~, ~*=~ \& ~/=~.

   105   - ~a1 + a2~

   106     does elements-wise addition.

   107     - Similarly ~-~, ~*~ \& ~/~.

   108   - ~a1 * a2~

   109     does element-wise multiplication

   110 

   111   *Note* - array(A) * array(B) does element wise multiplication and not matrix multiplication

   112 

   113 * Summary

   114   In this tutorial we covered,

   115   - Basics of arrays

   116   - Creating arrays

   117   - Arrays from lists

   118   - Basic array operations

   119 

   120 * Thank you!

   121 #+begin_latex

   122   \begin{block}{}

   123   \begin{center}

   124   This spoken tutorial has been produced by the

   125   \textcolor{blue}{FOSSEE} team, which is funded by the 

   126   \end{center}

   127   \begin{center}

   128     \textcolor{blue}{National Mission on Education through \\

   129       Information \& Communication Technology \\ 

   130       MHRD, Govt. of India}.

   131   \end{center}  

   132   \end{block}

   133 #+end_latex

   134 

   135