Matplot

MatplotLib - What and Why?

MatplotLib is a library for creating graphs in python

• Useful for creating data visualisations

• Can make it easy to understand complex data

• Can be combined with other modules like numpy and scipy

• Large number of options available

Bar Chart

One of the simplest plots we can create with MatplotLib is the bar chart. First we create a list of the names to go below each bar. We then create a list of corresponding values, where each value corresponds to the height of the bar chart. Then we use plt.bar()function to create the bar chart. Finally, we tell MatplotLib to show all of the charts that have been created using the plt.show() function.

import matplotlib.pyplot as plt

names = ['first', 'second', 'third']
values = [3, 1, 6]

plt.bar(names, values)
plt.show()

Line Graph

Line graphs can be created in a similar way, first a lists of x and corresponding y values are created. Then the plt.plot() function is used to create the graph.

import matplotlib.pyplot as plt

x = [1, 2, 3]
y = [1, 3, 6]

plt.plot(x, y)
plt.show()

Scatter Graph

Scatter graphs can be created in the same way as lien graphs, except that plt.scatter() is used instead of plt.plot().

import matplotlib.pyplot as plt

x = [1, 3, 2, 1.5]
y = [0, 5, 1, 4]

plt.scatter(x, y)
plt.show()

Formatting

The examples we have seen so far generate very basic plots with just the default options and no labeling. MatplotLib provides a number of functions to customise the appearance of appearance of plots.

import matplotlib.pyplot as plt

x = [1, 2, 3]
y = [1, 3, 6]

plt.plot(x, y)
plt.grid(True)
plt.xlabel('x axis')
plt.ylabel('y axis')
plt.title('This is a graph')
plt.show()