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17 #+LaTeX_HEADER:\lstset{language=Python, basicstyle=\ttfamily\bfseries, |
17 #+LaTeX_HEADER:\lstset{language=Python, basicstyle=\ttfamily\bfseries, |
18 #+LaTeX_HEADER: commentstyle=\color{red}\itshape, stringstyle=\color{darkgreen}, |
18 #+LaTeX_HEADER: commentstyle=\color{red}\itshape, stringstyle=\color{darkgreen}, |
19 #+LaTeX_HEADER: showstringspaces=false, keywordstyle=\color{blue}\bfseries} |
19 #+LaTeX_HEADER: showstringspaces=false, keywordstyle=\color{blue}\bfseries} |
20 |
20 |
21 #+TITLE: Accessing parts of arrays |
21 #+TITLE: Manipulating Lists |
22 #+AUTHOR: FOSSEE |
22 #+AUTHOR: FOSSEE |
23 #+EMAIL: |
23 #+EMAIL: |
24 #+DATE: |
24 #+DATE: |
25 |
25 |
26 #+DESCRIPTION: |
26 #+DESCRIPTION: |
27 #+KEYWORDS: |
27 #+KEYWORDS: |
28 #+LANGUAGE: en |
28 #+LANGUAGE: en |
29 #+OPTIONS: H:3 num:nil toc:nil \n:nil @:t ::t |:t ^:t -:t f:t *:t <:t |
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 |
30 #+OPTIONS: TeX:t LaTeX:nil skip:nil d:nil todo:nil pri:nil tags:not-in-toc |
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31 #+STARTUP: align fold nodlcheck hidestars oddeven lognotestate |
31 |
32 |
32 * Outline |
33 * Outline |
33 - Manipulating one and multi dimensional arrays |
34 In this session we shall be looking at |
34 - Access and change individual elements |
35 - Concatenating lists |
35 - Access and change rows and columns |
36 - Obtaining parts of lists |
36 - Slicing and striding on arrays to access chunks |
37 - Sorting lists |
37 - Read images into arrays and manipulations |
38 - Reversing lists |
38 * Sample Arrays |
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39 #+begin_src python |
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40 In []: A = array([12, 23, 34, 45, 56]) |
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41 |
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42 In []: C = array([[11, 12, 13, 14, 15], |
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43 [21, 22, 23, 24, 25], |
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44 [31, 32, 33, 34, 35], |
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45 [41, 42, 43, 44, 45], |
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46 [51, 52, 53, 54, 55]]) |
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47 |
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48 #+end_src |
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49 * Question 1 |
39 * Question 1 |
50 Change the last column of ~C~ to zeroes. |
40 Obtain the primes less than 10, from the list ~primes~. |
51 * Solution 1 |
41 * Solution 1 |
52 #+begin_src python |
42 #+begin_src python |
53 In []: C[:, -1] = 0 |
43 primes[0:4] |
54 #+end_src |
44 #+end_src python |
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45 * Slicing |
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46 #+begin_src python |
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47 p[start:stop] |
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48 #+end_src python |
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49 - Returns all elements of ~p~ between ~start~ and ~stop~ |
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50 - The element with index equal to ~stop~ is *not* included. |
55 * Question 2 |
51 * Question 2 |
56 Change ~A~ to ~[11, 12, 13, 14, 15]~. |
52 Obtain all the multiples of three from the list ~num~. |
57 * Solution 2 |
53 * Solution 2 |
58 #+begin_src python |
54 #+begin_src python |
59 In []: A[:] = [11, 12, 13, 14, 15] |
55 num[::3] |
60 #+end_src |
56 #+end_src python |
61 * squares.png |
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62 #+begin_latex |
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63 \begin{center} |
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64 \includegraphics[scale=0.6]{squares} |
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65 \end{center} |
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66 #+end_latex |
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67 * Question 3 |
57 * Question 3 |
68 - obtain ~[22, 23]~ from ~C~. |
58 Given a list of marks of students in an examination, obtain a list |
69 - obtain ~[11, 21, 31, 41]~ from ~C~. |
59 with marks in descending order. |
70 - obtain ~[21, 31, 41, 0]~. |
60 #+begin_src python |
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61 marks = [99, 67, 47, 100, 50, 75, 62] |
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62 #+end_src python |
71 * Solution 3 |
63 * Solution 3 |
72 #+begin_src python |
64 #+begin_src python |
73 In []: C[1, 1:3] |
65 sorted(marks)[::-1] |
74 In []: C[0:4, 0] |
66 #+end_src python |
75 In []: C[1:5, 0] |
67 OR |
76 #+end_src |
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77 * Question 4 |
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78 Obtain ~[[23, 24], [33, -34]]~ from ~C~ |
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79 * Solution 4 |
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80 #+begin_src python |
68 #+begin_src python |
81 In []: C[1:3, 2:4] |
69 sorted(marks, reverse=True) |
82 #+end_src |
70 #+end_src python |
83 * Question 5 |
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84 Obtain the square in the center of the image |
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85 * Solution 5 |
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86 #+begin_src python |
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87 In []: imshow(I[75:225, 75:225]) |
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88 #+end_src |
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89 * Question 6 |
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90 Obtain the following |
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91 #+begin_src python |
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92 [[12, 0], [42, 0]] |
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93 [[12, 13, 14], [0, 0, 0]] |
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94 #+end_src |
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95 |
71 |
96 * Solution 6 |
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97 #+begin_src python |
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98 In []: C[::3, 1::3] |
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99 In []: C[::4, 1:4] |
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100 #+end_src |
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101 * Summary |
72 * Summary |
102 You should now be able to -- |
73 In this tutorial session we learnt |
103 - Manipulate 1D \& Multi dimensional arrays |
74 + Obtaining parts of lists using slicing and striding |
104 - Access and change individual elements |
75 + List concatenation |
105 - Access and change rows and columns |
76 + Sorting lists |
106 - Slice and stride on arrays |
77 + Reversing lists |
107 - Read images into arrays and manipulate them. |
78 |
108 * Thank you! |
79 * Thank you! |
109 #+begin_latex |
80 #+begin_latex |
110 \begin{block}{} |
81 \begin{block}{} |
111 \begin{center} |
82 \begin{center} |
112 This spoken tutorial has been produced by the |
83 This spoken tutorial has been produced by the |