5.3 Bar Graphs and Pie Charts

Given frequency tables with two columns: categories/values and frequencies:

Syntax for bar graph

import matplotlib.pyplot as plt
value = [x1,x2,...]
freq = [y1,y2,...]
plt.bar(value,freq)

Syntax for pie chart

import matplotlib.pyplot as plt
value = [x1,x2,...]
freq = [y1,y2,...]
plt.pie(freq, labels=value,autopct='%1.1f%%' ) 

Example: 20 students were asked if they were registered to vote. Their responses are given below. Plot a bar graph.

Watch demo video

1. Click + Code
2. Type import matplotlib.pyplot as plt
3. Type v = ['Yes','No']
4. Type f = [11,9]
5. Type plt.bar(v,f)
6. Click play button
7. Right click image to save it to your device

import matplotlib.pyplot as plt
v = ['yes','no']
f = [11,9]
plt.bar(v,f)

<BarContainer object of 2 artists>

Example: 20 students were asked if they were registered to vote. Their responses are given below. Plot a pie chart (percent).

Watch demo video

1. Click + Code
2. Type import matplotlib.pyplot as plt
3. Type v = ['Yes','No']
4. Type f = [11,9]
5. Type plt.bar(f,labels=f,autopct='%1.1f%%')
6. Click play button
7. Right click on the image to save it to your device

Note: autopct='%1.1f%%' changes the frequency to percent rounded to one decimal place, and adds the percent sign %.

import matplotlib.pyplot as plt
v = ['yes','no']
f = [11,9]
plt.pie(f,labels=v,autopct='%1.1f%%')

([<matplotlib.patches.Wedge at 0x7fcbc206d1d0>,
  <matplotlib.patches.Wedge at 0x7fcbc202f3d0>],
 [Text(-0.17207795223283848, 1.086457168210212, 'yes'),
  Text(0.17207795223283862, -1.086457168210212, 'no')],
 [Text(-0.09386070121791189, 0.5926130008419338, '55.0%'),
  Text(0.09386070121791196, -0.5926130008419338, '45.0%')])

Example: 20 students were asked if they were registered to vote. Their responses are given below. Plot a bar graph.

Add title, vertical and horizontal labels.

1. Click + Code
2. Type import matplotlib.pyplot as plt
3. Type v = ['Yes','No']
4. Type f = [11,9]
5. Type plt.bar(v,f)
6. Type plt.suptitle("Voter Registation")
7. Type plt.xlabel("Registration")
8. Type plt.ylabel("Frequency")
9. Click play button

import matplotlib.pyplot as plt
v = ['yes','no']
f = [11,9]
plt.bar(v,f)
plt.suptitle("Voter Registration")
plt.xlabel("Registration")
plt.ylabel("Frequency")

Text(0, 0.5, 'Frequency')

Example: The frequency distribution below is the waiting time, in minutes, of 20 customers at a fast food restaurant.

Plot a bar graph and a pie chart.

Note: First the data values in the two columns are entered separately using Python lists: waiting_time and frequency.

1. Click + Code
2. Type import matplotlib.pyplot as plt
3. Type waiting_time = [1,2,3,4,5,6]
4. Type frequency = [2,3,4,5,5,1]
5. Type plt.bar(waiting_time,frequency)
6. Type plt.xlabel("Waiting Time")
7. Type plt.ylabel("Frequency")
8. Click play button

import matplotlib.pyplot as plt

waiting_time = [1,2,3,4,5,6]        
frequency = [2,3,4,5,5,1]      

plt.bar(waiting_time,frequency)        

plt.xlabel("Waiting Time")
plt.ylabel("Frequency")

Text(0, 0.5, 'Frequency')

Example: The frequency distribution below is the waiting time, in minutes, of 20 customers at a fast food restaurant.

Graph a Pie Chart

import matplotlib.pyplot as plt

waiting_time = [1,2,3,4,5,6]        
frequency = [2,3,4,5,5,1]      
plt.pie(frequency, labels=waiting_time,autopct='%1.1f%%')        
plt.xlabel("Waiting Time")

Text(0.5, 0, 'Waiting Time')

Adapted from Python for Introductory Statistics, by Simon Aman (Truman College, City Colleges of Chicago), licensed under CC BY 4.0. Changes were made: reformatted as an accessible XYZ web edition with live in-browser code cells. License: CC-BY-4.0.