Part 1: Introduction to Plotting

Plotting with `matplotlib`

In CS111, we will use Python’s matplotlib library to make plots/graphs/charts.

Reference materials:

We'll need to import these modules whenever we want to plot:

import matplotlib.pyplot as plt
import numpy as np

Line plots

plt.figure(figsize=(3,3))
plt.plot([10, 20, 15])
plt.show()

Draw the plot here:

Note: plot allows you to specify the following:

color = 'r'
linestyle = 'dashed'
linewidth = 5

plt.figure(figsize=(3, 3))
plt.plot([1, 3, 5, 7, 9], [5, 1, 3, 1, 5], color='r', linewidth=4)
plt.show()

Draw the plot here:

Controlling axes with axis/xlim/ylim

x = [1, 3, 5, 7, 9]
y = [5, 1, 3, 1, 5]
plt.figure(figsize=(3, 3))
plt.plot(x, y, 'r-.', lw=5) # shortcut for red dash-dot line, linewidth 5
plt.axis([0, 10, 0, 6]) # list with xmin, xmax, ymin, ymax
plt.show()

x = [1, 3, 5, 7, 9]
y = [5, 1, 3, 1, 5]
plt.figure(figsize=(3, 3))
plt.plot(x, y, 'c:', lw=3) # cyan dotted line, linewidth 3
plt.ylim((-10, 10)) # tuple
plt.show()

Adding descriptive text to plot (title, axis & tick labels)

plt.figure(figsize=(4.5, 4.5))

plt.plot(x, y, 'b-.', lw=5)
plt.axis([0, 10, 0, 6])
plt.xticks([1, 5, 9], 
           ['x:p1', 'x:p3', 'x:p5'])
plt.yticks([5, 3, 1], 
           ['y:p1,p5', 'y:pt3', 'y:p2,p4'],
           rotation=90)
plt.xlabel("width for letter W")
plt.ylabel("height for letter W")
plt.title("W is for Wellesley", fontsize=14)
plt.show()

Pre-defined style sheets

Examples in our slide reference use ggplot.

plt.style.use('ggplot')

Interested in other style sheets? Here is a visual matplotlib style sheet reference.

No style sheet	ggplot stylesheet