Diverging bar charts in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple diverging bar chart code

What will be the output of this Python code using matplotlib to create a diverging bar chart?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np

labels = ['A', 'B', 'C', 'D']
values = np.array([3, -2, 5, -1])
colors = ['green' if x > 0 else 'red' for x in values]

plt.bar(labels, values, color=colors)
plt.axhline(0, color='black')
plt.show()

A A line chart connecting points A, B, C, D with values 3, -2, 5, -1.

B A bar chart with all bars in blue, some going up and some going down, with no horizontal line.

C A scatter plot with points at (A,3), (B,-2), (C,5), (D,-1) colored green and red.

D A bar chart with bars for A and C going up in green, bars for B and D going down in red, and a black horizontal line at zero.

💡 Hint

Look at how colors are assigned based on positive or negative values and the use of axhline.

The code creates a bar chart where positive values are green bars going upwards, negative values are red bars going downwards, and a black horizontal line at zero separates positive and negative bars.

❓ data_output

intermediate

Number of bars above and below zero

Given the following data and code for a diverging bar chart, how many bars will be above zero and how many below zero?

Matplotlib

import numpy as np
values = np.array([10, -5, 0, 3, -7, 2])

A Above zero: 3 bars; Below zero: 2 bars

B Above zero: 4 bars; Below zero: 2 bars

C Above zero: 3 bars; Below zero: 3 bars

D Above zero: 2 bars; Below zero: 3 bars

💡 Hint

Count values strictly greater than zero and strictly less than zero. Zero is neither.

Values above zero are 10, 3, and 2 (3 bars). Values below zero are -5 and -7 (2 bars). Zero is not counted.

❓ visualization

advanced

Identify the correct diverging bar chart visualization

Which of the following code snippets produces a diverging bar chart with labels on the y-axis and horizontal bars diverging from zero?

A plt.scatter(labels, values, color='red')

B plt.barh(labels, values, color=['red' if v < 0 else 'blue' for v in values]); plt.axvline(0, color='black')

C plt.plot(labels, values, color='blue')

D plt.bar(labels, values, color=['red' if v < 0 else 'blue' for v in values]); plt.axhline(0, color='black')

💡 Hint

Think about which function creates horizontal bars and where the zero line should be.

plt.barh creates horizontal bars. The zero line for horizontal bars is vertical, so axvline is used. This matches option B.

🔧 Debug

advanced

Identify the error in diverging bar chart code

What error will this code raise?

import matplotlib.pyplot as plt
values = [4, -3, 2, -1]
colors = ['green' if x > 0 else 'red' for x in values]
plt.bar(range(len(values)), values, color=colors)
plt.axhline(0, color='black')
plt.show()

A No error; the code runs and shows a diverging bar chart.

B TypeError because colors list length does not match bars.

C ValueError because plt.bar expects labels, not range indices.

D NameError because 'plt' is not imported.

💡 Hint

Check if the colors list length matches the number of bars and if imports are correct.

The code runs correctly because the colors list matches the number of bars, and plt is imported. Using range(len(values)) for x-axis is valid.

🚀 Application

expert

Calculate net positive and negative sums from diverging bar chart data

Given the following data representing changes in sales (positive and negative), what are the total positive and total negative sums?

sales_changes = [15, -7, 0, 8, -3, -5, 12]

A Total positive sum: 27; Total negative sum: -15

B Total positive sum: 35; Total negative sum: -10

C Total positive sum: 35; Total negative sum: -15

D Total positive sum: 27; Total negative sum: -10

💡 Hint

Add only positive numbers for positive sum, and only negative numbers for negative sum.

Positive values: 15 + 8 + 12 = 35 is correct because 0 is not positive. Negative values: -7 + -3 + -5 = -15. So total positive sum is 35, total negative sum is -15. Option C says 27 positive sum, which is incorrect. So correct is option C.