Area chart with plt.fill_between in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of plt.fill_between with simple data

What will be the output of this code snippet that uses plt.fill_between to create an area chart?

Matplotlib

import matplotlib.pyplot as plt
x = [1, 2, 3, 4]
y = [2, 3, 5, 7]
plt.fill_between(x, y, color='skyblue')
plt.show()

A An error because plt.fill_between requires three arguments

B A line plot connecting points (1,2), (2,3), (3,5), (4,7) without any shaded area

C A blue shaded area under the curve connecting points (1,2), (2,3), (3,5), (4,7)

D A scatter plot of points (1,2), (2,3), (3,5), (4,7) with blue dots

💡 Hint

Remember, plt.fill_between fills the area between the x-axis and the y-values.

The function plt.fill_between fills the area between the x-axis (default y=0) and the y-values given. Here, it creates a blue shaded area under the curve defined by points (x, y).

🧠 Conceptual

intermediate

Understanding the role of y2 in plt.fill_between

In plt.fill_between(x, y1, y2), what does the parameter y2 represent?

A The lower boundary of the filled area

B The upper boundary of the filled area

C The color of the filled area

D The x-axis values

💡 Hint

Think about the area being filled between two curves.

In plt.fill_between, y1 and y2 define the two boundaries between which the area is filled. y1 is the upper boundary by default, and y2 is the lower boundary. If y2 is omitted, it defaults to zero (the x-axis).

🔧 Debug

advanced

Identify the error in this plt.fill_between usage

What error will this code produce and why?

import matplotlib.pyplot as plt
x = [0, 1, 2, 3]
y1 = [1, 2, 3]
y2 = [0, 1, 1, 2]
plt.fill_between(x, y1, y2)
plt.show()

A IndexError because x is shorter than y2

B TypeError because y1 and y2 must be numpy arrays

C No error, the plot will display correctly

D ValueError due to mismatched lengths of x and y1

💡 Hint

Check if all input lists have the same length.

The lists x and y1 have different lengths (4 vs 3), which causes a ValueError because plt.fill_between requires all input arrays to have the same length.

❓ data_output

advanced

Resulting data from plt.fill_between with condition

Given this code, what is the number of points where the area is filled?

import numpy as np
import matplotlib.pyplot as plt
x = np.arange(5)
y1 = np.array([1, 3, 2, 5, 4])
y2 = np.array([0, 2, 1, 3, 2])
plt.fill_between(x, y1, y2, where=(y1 > y2))
plt.show()

A 0 points because y1 is never greater than y2

B 5 points where y1 is greater than y2

C 2 points where y1 is less than y2

D 3 points where y1 is greater than y2

💡 Hint

Compare y1 and y2 values element-wise.

All elements in y1 are greater than corresponding elements in y2, so the area is filled for all 5 points.

🚀 Application

expert

Visualizing overlapping areas with plt.fill_between

You want to visualize two overlapping datasets using plt.fill_between. Which code snippet correctly fills the area between two curves y1 and y2 with different colors for the overlapping and non-overlapping regions?

Matplotlib

import numpy as np
import matplotlib.pyplot as plt
x = np.linspace(0, 10, 100)
y1 = np.sin(x) + 1
y2 = 0.5 * np.cos(x) + 1

# Which option correctly colors overlapping and non-overlapping areas?

A

plt.fill_between(x, y1, y2, where=(y1 >= y2), color='blue', alpha=0.5)
plt.fill_between(x, y1, y2, where=(y1 < y2), color='red', alpha=0.5)
plt.show()

B

plt.fill_between(x, y1, y2, color='blue', alpha=0.5)
plt.fill_between(x, y2, y1, color='red', alpha=0.5)
plt.show()

C

plt.fill_between(x, y1, y2, where=(y1 > y2), color='red')
plt.fill_between(x, y1, y2, where=(y1 <= y2), color='blue')
plt.show()

D

plt.fill_between(x, y1, y2, color='green')
plt.fill_between(x, y2, y1, color='yellow')
plt.show()

💡 Hint

Use the 'where' parameter to separate regions based on condition.

Option A uses the 'where' parameter to fill the area between y1 and y2 with blue where y1 >= y2 and red where y1 < y2, correctly showing overlapping and non-overlapping areas with different colors.