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20 |
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21 #+TITLE: Getting started with arrays |
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22 #+AUTHOR: FOSSEE |
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23 #+EMAIL: info@fossee.in |
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24 #+DATE: |
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25 |
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26 #+DESCRIPTION: |
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27 #+KEYWORDS: |
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28 #+LANGUAGE: en |
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29 #+OPTIONS: H:3 num:nil toc:nil \n:nil @:t ::t |:t ^:t -:t f:t *:t <:t |
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30 #+OPTIONS: TeX:t LaTeX:nil skip:nil d:nil todo:nil pri:nil tags:not-in-toc |
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31 |
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32 * Outline |
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33 - Arrays |
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34 - why arrays over lists |
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35 - Creating arrays |
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36 - Array operations |
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37 |
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38 * Overview of Arrays |
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39 - Arrays are homogeneous data structures. |
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40 - elements have to the same data type |
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41 - Arrays are faster compared to lists |
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42 - at least /80-100 times/ faster than lists |
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43 |
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44 * Creating Arrays |
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45 - Creating a 1-dimensional array |
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46 : In []: a1 = array([1, 2, 3, 4]) |
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47 ~[1, 2, 3, 4]~ is a list. |
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48 * Creating two-dimensional array |
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49 - Creating a 2-dimensional array |
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50 : In []: a2 = array([[1,2,3,4],[5,6,7,8]]) |
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51 here we convert a list of lists to an array making a 2-d array. |
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52 - Using ~arange()~ function |
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53 : In []: ar = arange(1,9) |
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54 * ~reshape()~ method |
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55 - To reshape an array |
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56 : In []: ar.reshape(2, 4) |
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57 : In []: ar.reshape(4, 2) |
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58 : In []: ar = ar.reshape(2, 4) |
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59 |
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60 * Creating ~array~ from ~list~. |
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61 - ~array()~ method accepts list as argument |
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62 - Creating a list |
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63 : In []: l1 = [1, 2, 3, 4] |
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64 - Creating an array |
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65 : In []: a3 = array(l1) |
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66 |
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67 * Exercise 1 |
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68 Create a 3-dimensional array of the order (2, 2, 4). |
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69 |
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70 * ~.shape~ of array |
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71 - ~.shape~ |
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72 To find the shape of the array |
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73 : In []: a2.shape |
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74 - ~.shape~ |
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75 returns a tuple of shape |
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76 * Exercise 2 |
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77 Find out the shape of the other arrays(a1, a3, ar) that we have created. |
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78 * Homogeneous data |
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79 - All elements in array should be of same type |
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80 : In []: a4 = array([1,2,3,'a string']) |
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81 * Implicit type casting |
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82 : In []: a4 |
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83 All elements are type casted to string type |
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84 * ~identity()~, ~zeros()~ methods |
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85 - ~identity(n)~ |
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86 Creates an identity matrix, a square matrix of order (n, n) with diagonal elements 1 and others 0. |
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87 - ~zeros((m, n))~ |
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88 Creates an ~m X n~ matrix with all elements 0. |
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89 |
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90 * Learning exercise |
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91 - Find out about |
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92 - ~zeros_like()~ |
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93 - ~ones()~ |
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94 - ~ones_like()~ |
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95 |
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96 * Array operations |
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97 - ~a1 * 2~ |
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98 returns a new array with all elements of ~a1~ multiplied by ~2~. |
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99 - Similarly ~+~, ~-~ \& ~/~. |
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100 - ~a1 + 2~ |
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101 returns a new array with all elements of ~a1~ summed with ~2~. |
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102 - ~a1 += 2~ |
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103 adds ~2~ to all elements of array ~a1~. |
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104 - Similarly ~-=~, ~*=~ \& ~/=~. |
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105 - ~a1 + a2~ |
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106 does elements-wise addition. |
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107 - Similarly ~-~, ~*~ \& ~/~. |
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108 - ~a1 * a2~ |
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109 does element-wise multiplication |
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110 |
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111 *Note* - array(A) * array(B) does element wise multiplication and not matrix multiplication |
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112 |
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113 * Summary |
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114 In this tutorial we covered, |
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115 - Basics of arrays |
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116 - Creating arrays |
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117 - Arrays from lists |
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118 - Basic array operations |
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119 |
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120 * Thank you! |
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121 #+begin_latex |
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122 \begin{block}{} |
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123 \begin{center} |
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124 This spoken tutorial has been produced by the |
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125 \textcolor{blue}{FOSSEE} team, which is funded by the |
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126 \end{center} |
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127 \begin{center} |
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128 \textcolor{blue}{National Mission on Education through \\ |
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129 Information \& Communication Technology \\ |
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130 MHRD, Govt. of India}. |
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131 \end{center} |
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132 \end{block} |
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133 #+end_latex |
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134 |
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135 |