4 |
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5 Welcome to this tutorial on loading data from files. |
5 Welcome to this tutorial on loading data from files. |
6 |
6 |
7 {{{ Screen shows welcome slide }}} |
7 {{{ Screen shows welcome slide }}} |
8 |
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9 Until now, all the plots we have made use analytic functions. We have |
9 We often require to plot points obtained from experimental |
10 been using analytic functions to generate a sequence of points and |
10 observations. In this tutorial we shall learn to read data from files |
11 plotting them, against another sequence of points. But, this is not |
11 and save it into sequences that can later be used to plot. |
12 what we do most often. We often require to plot points obtained from |
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13 experimental observations. |
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14 |
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15 .. #[punch: the initial part of the paragraph may be removed, to make |
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16 this a more generic LO?] |
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17 |
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18 .. #[Nishanth]: The paragraph can be removed. |
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19 |
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20 In this tutorial we shall learn to read data from files and save it |
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21 into sequences that can later be used to plot. |
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22 |
12 |
23 {{{ Show the outline for this tutorial }}} |
13 {{{ Show the outline for this tutorial }}} |
24 |
14 |
25 We shall use the ``loadtxt`` command to load data from files. We will |
15 We shall use the ``loadtxt`` command to load data from files. We will |
26 be looking at how to get multiple columns of data into multiple |
16 be looking at how to read a file with multiple columns of data and |
27 sequences. |
17 load each column of data into a sequence. |
28 |
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29 .. #[Nishanth]: can be "How to read a file with multiple columns of |
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30 data and load each column of data into a sequence." |
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31 |
18 |
32 {{{ switch back to the terminal }}} |
19 {{{ switch back to the terminal }}} |
33 |
20 |
34 As usual, let us start IPython, using |
21 As usual, let us start IPython, using |
35 :: |
22 :: |
36 |
23 |
37 ipython -pylab |
24 ipython -pylab |
38 |
25 |
39 Now, Let us begin with reading the file primes.txt, which contains |
26 Now, Let us begin with reading the file primes.txt, which contains |
40 just a list of primes listed in a column, using the loadtxt command. |
27 just a list of primes listed in a column, using the loadtxt command. |
41 The file, in our case, is present in ``/home/fossee/primes.txt``. |
28 The file, in our case, is present in ``/home/fossee/primes.txt``. |
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29 |
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30 {{{ Navigate to the path in the OS, open the file and show it }}} |
42 |
31 |
43 .. #[punch: do we need a slide for showing the path?] |
32 .. #[punch: do we need a slide for showing the path?] |
44 |
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45 We use the ``cat`` command to see the contents of this file. |
34 .. We use the ``cat`` command to see the contents of this file. |
46 |
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47 #[punch: should we show the cat command here? seems like a good place |
36 .. #[punch: should we show the cat command here? seems like a good place |
48 to do it] :: |
37 to do it] :: |
49 |
38 |
50 cat /home/fossee/primes.txt |
39 cat /home/fossee/primes.txt |
51 |
40 |
52 .. #[Nishanth]: A problem for windows users. |
41 .. #[Nishanth]: A problem for windows users. |
53 Should we simply open the file and show them the data |
42 Should we simply open the file and show them the data |
54 so that we can be fine with GNU/Linux ;) and windows? |
43 so that we can be fine with GNU/Linux ;) and windows? |
55 |
44 |
116 |
105 |
117 .. #[Nishanth]: Stress on ``unpack=True`` ?? |
106 .. #[Nishanth]: Stress on ``unpack=True`` ?? |
118 |
107 |
119 Notice, that L and T now contain the first and second columns of data |
108 Notice, that L and T now contain the first and second columns of data |
120 from the data file, ``pendulum.txt``, and they are both simple |
109 from the data file, ``pendulum.txt``, and they are both simple |
121 sequences. |
110 sequences. ``unpack=True`` has given us the two columns in to two |
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111 separate sequences instead of one complex sequence. |
122 |
112 |
123 {{{ show the slide with loadtxt --- other features }}} |
113 {{{ show the slide with loadtxt --- other features }}} |
124 |
114 |
125 In this tutorial, we have learnt the basic use of the ``loadtxt`` |
115 In this tutorial, we have learnt the basic use of the ``loadtxt`` |
126 command, which is capable of doing a lot more than we have used it for |
116 command, which is capable of doing a lot more than we have used it for |
133 finished, resume the video to look at the solution. |
123 finished, resume the video to look at the solution. |
134 |
124 |
135 {{{ switch back to the terminal }}} |
125 {{{ switch back to the terminal }}} |
136 :: |
126 :: |
137 |
127 |
138 L, T = loadtxt('/home/fossee/pendulum.txt', unpack=True, delimiter=';') |
128 L, T = loadtxt('/home/fossee/pendulum_semicolon.txt', unpack=True, delimiter=';') |
139 |
129 |
140 print L |
130 print L |
141 |
131 |
142 print T |
132 print T |
143 |
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144 .. #[Nishanth]: L, T = loadtxt('/home/fossee/pendulum_semicolon.txt', ...) |
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145 |
133 |
146 This brings us to the end of this tutorial. |
134 This brings us to the end of this tutorial. |
147 |
135 |
148 {{{ show the summary slide }}} |
136 {{{ show the summary slide }}} |
149 |
137 |