matplotlib Plotting Cookbook

Plotting curves from file data

As explained earlier, matplotlib only handles plotting. If you want to plot data stored in a file, you will have to use Python code to read the file and extract the data you need.

How to do it...

Let's assume that we have time series stored in a plain text file named my_data.txt as follows:

0  0
1  1
2  4
4 16
5 25
6 36

A minimalistic pure Python approach to read and plot that data would go as follows:

import matplotlib.pyplot as plt

X, Y = [], []
for line in open('my_data.txt', 'r'):
  values = [float(s) for s in line.split()]
  X.append(values[0])
  Y.append(values[1])

plt.plot(X, Y)
plt.show()

This script, together with the data stored in my_data.txt, will produce the following graph:

How it works...

The following are some explanations ...