Introduction to Matplotlib

Chapter:6

Data Visualization

Introduction to Matplotlib

•  Matplotlib is an open source drawing library. We can use it freely.

•  We can generate plots, histograms, bar charts and other types of charts with few lines of codes.

•  Matplotlib was created by John D. Hunter.

• Matplotlib is mostly written in Python and few segments are written in C and JavaScript.

Features of Matplotlib

1) It is a powerful tool for data analysis.

2) It is flexible and support various forms of data representations.

3) It is easy to access large amount of data using Matplotlib.

4) It is customizable.

5) It can run on different platforms.

6) It is useful in creating advanced visualizations

7) It is easy to learn and understand.

8) Being open‒source platform it saves the cost.

Installation

•  If a Python and Pip is already installed on a system then for installation of Matplotlib following command can be issued at the command prompt

Prompt> pip install matplotlib

• If the Python Distribution like Anaconda is already installed on your PC then the Matplotlib comes by default and there is no need to install it.

Import

• For using the functionalities offered by the Matplotlib we need to import it first.

In [1]: import matplotlib

Matplotlib Pyplot

•  pyplot is a matplotlib module that provides simple functions for adding plot elements, such as lines, images, text, etc.

• Most of the utilities of Matplotlib lie under plyplot submodule and are imported using plt as alias.

• For using plyplot submodule we write following statement at the beginning of Python script from matplotlib import plyplot as plt

or alternatively we can write as

import matplotlib.pyplot as plt

• Following example illustrates the use of plyplot for drawing a line

In [7]: from matplotlib import pyplot as plt

plt.plot([0,10], [0,100])

plt.show()

Output

Concept of plot in Matplotlib

• The plot() function is used to draw points in a graph. By default plot() function draws line from point to point.

plt.plot(x‒axis_points, y‒axis_points)

• The x‒axis is the horizontal axis and y‒axis is the vertical axis.

Plotting without a line

• To plot only the markers, we can use shortcut string notation parameter 'o', which means 'rings'.

In [15]: from matplotlib import pyplot as plt

plt.plot([0,10], [10, 10], 'o')

plt.show()

Output

Plot using multiple points

• We can make use of array of points to draw the multiple lines. For creating an array we normally use NumPy and for plotting the lines we use Matplotlib. For example ‒

Example:1

Draw lines (1,7),(2,4), (3,15),(4,10)

Solution:

In [16]: from matplotlib import pyplot as plt

import numpy as np

x = np.array([1,2,3,4])

y = np.array([7,4,15,10])

plt.plot(x,y)

plt.show()

Output