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POFinding moving average from data points in Python
 

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  1. POFinding moving average from data points in Python
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    <p>I am playing in Python a bit again, and I found a neat book with examples. One of the examples is to plot some data. I have a .txt file with two columns and I have the data. I plotted the data just fine, but in the exercise it says: Modify your program further to calculate and plot the running average of the data, defined by:</p> <pre><code>$Y_k=\frac{1}{2r}\sum_{m=-r}^r y_{k+m}$ </code></pre> <p>where <code>r=5</code> in this case (and the <code>y_k</code> is the second column in the data file). Have the program plot both the original data and the running average on the same graph.</p> <p>So far I have this:</p> <pre><code>from pylab import plot, ylim, xlim, show, xlabel, ylabel from numpy import linspace, loadtxt data = loadtxt("sunspots.txt", float) r=5.0 x = data[:,0] y = data[:,1] plot(x,y) xlim(0,1000) xlabel("Months since Jan 1749.") ylabel("No. of Sun spots") show() </code></pre> <p>So how do I calculate the sum? In Mathematica it's simple since it's symbolic manipulation (Sum[i, {i,0,10}] for example), but how to calculate sum in python which takes every ten points in the data and averages it, and does so until the end of points?</p> <p>I looked at the book, but found nothing that would explain this :\</p> <hr> <p>heltonbiker's code did the trick ^^ :D</p> <pre><code>from __future__ import division from pylab import plot, ylim, xlim, show, xlabel, ylabel, grid from numpy import linspace, loadtxt, ones, convolve import numpy as numpy data = loadtxt("sunspots.txt", float) def movingaverage(interval, window_size): window= numpy.ones(int(window_size))/float(window_size) return numpy.convolve(interval, window, 'same') x = data[:,0] y = data[:,1] plot(x,y,"k.") y_av = movingaverage(y, 10) plot(x, y_av,"r") xlim(0,1000) xlabel("Months since Jan 1749.") ylabel("No. of Sun spots") grid(True) show() </code></pre> <p>And I got this: </p> <p><img src="https://i.stack.imgur.com/4TyaF.png" alt="image"></p> <p>Thank you very much ^^ :)</p>
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    1. COThat's weird. Since we don't have your txt file, it's not possible to test here, but I think the `xlim` line should not be used (just in case)
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    2. COI got the points from here: http://www-personal.umich.edu/~mejn/computational-physics/sunspots.dat And removing xlim didn't help :\
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    3. COI made a mistake in the code! you have to perform the average on the y array, not x: `y_av = movingaverage(y, r)` `plot(x, y_av)`. And you can use xlim again, I think.
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