Bar chart color customization in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Bar chart with single color

What color will the bars be in this matplotlib bar chart code?

Matplotlib

import matplotlib.pyplot as plt

values = [3, 7, 5]
labels = ['A', 'B', 'C']
plt.bar(labels, values, color='green')
plt.show()

A Blue bars

B Green bars

C Red bars

D Bars with default color (blue)

💡 Hint

Look at the color argument in plt.bar function.

The color parameter is set to 'green', so all bars will be green.

❓ data_output

intermediate

Bar chart with list of colors

What colors will the bars have in this matplotlib code?

Matplotlib

import matplotlib.pyplot as plt

values = [4, 6, 8]
labels = ['X', 'Y', 'Z']
colors = ['red', 'blue', 'yellow']
plt.bar(labels, values, color=colors)
plt.show()

A Bars colored red, blue, yellow respectively

B All bars red

C Bars colored blue, red, yellow respectively

D Bars colored yellow, blue, red respectively

💡 Hint

The color argument accepts a list matching bars order.

Each bar gets the color from the list in order: first red, then blue, then yellow.

❓ visualization

advanced

Custom color for bars based on value

Which option produces a bar chart where bars with values above 5 are red, others are green?

Matplotlib

import matplotlib.pyplot as plt

values = [2, 7, 4, 9]
labels = ['P', 'Q', 'R', 'S']
colors = ['red' if v > 5 else 'green' for v in values]
plt.bar(labels, values, color=colors)
plt.show()

A Bars with values > 5 are green, others red

B All bars are green

C Bars alternate red and green regardless of value

D Bars with values > 5 are red, others green

💡 Hint

Look at the list comprehension for colors.

The list comprehension sets 'red' for values above 5, else 'green'.

🔧 Debug

advanced

Identify error in bar color assignment

What error occurs when running this code?

Matplotlib

import matplotlib.pyplot as plt

values = [1, 2, 3]
labels = ['a', 'b', 'c']
colors = 'red, blue, green'
plt.bar(labels, values, color=colors)
plt.show()

A TypeError because color expects a list, not a string

B SyntaxError due to missing brackets

C No error, bars colored red, blue, green

D ValueError because colors list length mismatch

💡 Hint

Check the type of colors variable.

colors is a single string, not a list, so matplotlib cannot assign colors per bar.

🚀 Application

expert

Create a bar chart with gradient colors

Which code snippet correctly creates a bar chart with bars colored from light blue to dark blue using matplotlib?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np

values = [5, 10, 15, 20]
labels = ['W', 'X', 'Y', 'Z']
# Fill in the color assignment
colors = [plt.cm.Blues(i) for i in np.linspace(0.3, 1, len(values))]
plt.bar(labels, values, color=colors)
plt.show()

A colors = plt.cm.Blues(np.linspace(0.3, 1, len(values)))

B colors = ['lightblue', 'blue', 'darkblue', 'navy']

C colors = [plt.cm.Blues(i) for i in np.linspace(0.3, 1, len(values))]

D colors = [plt.cm.Blues(i) for i in range(len(values))]

💡 Hint

Use a colormap with values between 0 and 1 for gradient.

Option C uses np.linspace to generate evenly spaced values between 0.3 and 1, then maps them to the Blues colormap, producing a gradient.