Inverted axes in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this inverted x-axis plot code?

Consider the following Python code using matplotlib. What will be the x-axis limits after running this code?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([1, 2, 3, 4], [10, 20, 25, 30])
plt.gca().invert_xaxis()
limits = plt.gca().get_xlim()
print(limits)

A print outputs (4.0, 1.0)

B print outputs (1.0, 4.0)

C print outputs (10.0, 30.0)

D print outputs (30.0, 10.0)

💡 Hint

Remember that invert_xaxis() reverses the x-axis limits.

The invert_xaxis() method reverses the x-axis limits. Since the original x-axis limits are (1.0, 4.0), after inversion they become (4.0, 1.0).

❓ data_output

intermediate

What is the y-axis range after inversion?

Given this code snippet, what will be the y-axis limits printed?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([0, 1, 2], [5, 10, 15])
plt.gca().invert_yaxis()
limits = plt.gca().get_ylim()
print(limits)

A print outputs (5.0, 15.0)

B print outputs (15.0, 5.0)

C print outputs (0.0, 2.0)

D print outputs (2.0, 0.0)

💡 Hint

invert_yaxis() reverses the y-axis limits.

The original y-axis limits are (5.0, 15.0). After invert_yaxis(), the limits become (15.0, 5.0).

❓ visualization

advanced

Which plot shows the x-axis inverted correctly?

You have four plots showing the same data but with different axis settings. Which plot correctly inverts the x-axis?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np
x = np.arange(5)
y = x**2
fig, axs = plt.subplots(2, 2)

# Plot A
axs[0,0].plot(x, y)
axs[0,0].set_title('A')

# Plot B
axs[0,1].plot(x, y)
axs[0,1].invert_xaxis()
axs[0,1].set_title('B')

# Plot C
axs[1,0].plot(x, y)
axs[1,0].invert_yaxis()
axs[1,0].set_title('C')

# Plot D
axs[1,1].plot(x, y)
axs[1,1].invert_xaxis()
axs[1,1].invert_yaxis()
axs[1,1].set_title('D')

plt.tight_layout()
plt.show()

A Plot D

B Plot A

C Plot C

D Plot B

💡 Hint

invert_xaxis() flips the x-axis direction.

Only Plot B uses invert_xaxis() alone, which correctly inverts the x-axis. Plot D inverts both axes, Plot C inverts only y-axis, and Plot A has no inversion.

🧠 Conceptual

advanced

What happens if you invert both axes twice?

If you call invert_xaxis() and invert_yaxis() twice each on the same plot, what will be the final axis directions?

A Both axes will be inverted once, so both axes reversed

B Only x-axis will be inverted, y-axis normal

C Both axes will return to normal direction (not inverted)

D Only y-axis will be inverted, x-axis normal

💡 Hint

Inverting an axis twice cancels the inversion.

Calling invert_xaxis() or invert_yaxis() toggles the axis direction. Doing it twice returns the axis to its original direction.

🔧 Debug

expert

Why does this code not invert the x-axis as expected?

This code attempts to invert the x-axis but the plot shows normal x-axis direction. What is the reason?

Matplotlib

import matplotlib.pyplot as plt
plt.plot([1, 2, 3], [4, 5, 6])
plt.invert_xaxis()
plt.show()

A plt.invert_xaxis() is not a valid function; invert_xaxis() must be called on the Axes object

B The plot data is too small to show inversion

C invert_xaxis() only works after plt.show()

D The x-axis is inverted but the y-axis is overriding it

💡 Hint

Check where invert_xaxis() is called from.

invert_xaxis() is a method of the Axes object, not the pyplot module. Calling plt.invert_xaxis() causes an AttributeError and does not invert the axis.

Practice

1. What does the invert_xaxis() method do in a matplotlib plot?

easy

A. It changes the x-axis scale from linear to logarithmic.

B. It swaps the x-axis with the y-axis.

C. It hides the x-axis labels and ticks.

D. It reverses the direction of the x-axis, so values decrease from left to right.

Solution

1. Step 1: Understand the purpose of invert_xaxis()

   The method invert_xaxis() reverses the x-axis direction, making values decrease from left to right instead of increasing.

2. Step 2: Compare with other options

   Options A, C, and D describe different actions unrelated to axis inversion.

3. Final Answer:

   It reverses the direction of the x-axis, so values decrease from left to right. -> Option D

4. Quick Check:

   invert_xaxis() reverses x-axis direction [OK]

Hint: invert_xaxis() flips x-axis direction left to right [OK]

Common Mistakes:

• Confusing invert_xaxis() with changing scale
• Thinking it hides axis labels
• Assuming it swaps axes

2. Which of the following is the correct way to invert the y-axis in matplotlib?

easy

A. plt.invert_yaxis()

B. ax.axis.invert_y()

C. ax.invert_yaxis()

D. plt.axis('invert_y')

Solution

1. Step 1: Recall the correct syntax for axis inversion

   In matplotlib, axis inversion methods are called on the axis object, not directly on plt.

2. Step 2: Identify the correct method call

   The correct method is invert_yaxis() called on an axis object, typically named ax.

3. Final Answer:

   ax.invert_yaxis() -> Option C

4. Quick Check:

   Use ax.invert_yaxis() to invert y-axis [OK]

Hint: Call invert_yaxis() on axis object, not plt [OK]

Common Mistakes:

• Calling invert_yaxis() on plt instead of ax
• Using incorrect method names
• Trying to invert axis via plt.axis()

3. What will be the effect of the following code snippet?

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([1, 2, 3], [10, 20, 30])
ax.invert_xaxis()
plt.show()

medium

A. The x-axis will display values from 3 to 1 left to right.

B. The x-axis will display values from 1 to 3 left to right.

C. The y-axis will be inverted, showing 30 to 10 bottom to top.

D. The plot will raise an error because invert_xaxis() is invalid.

Solution

1. Step 1: Analyze the code's axis inversion

   The code calls ax.invert_xaxis(), which reverses the x-axis direction.

2. Step 2: Understand axis direction after inversion

   Normally, x-axis goes from 1 to 3 left to right; after inversion, it goes from 3 to 1 left to right.

3. Final Answer:

   The x-axis will display values from 3 to 1 left to right. -> Option A

4. Quick Check:

   invert_xaxis() reverses x-axis values [OK]

Hint: invert_xaxis() flips x-axis values order [OK]

Common Mistakes:

• Thinking invert_xaxis() affects y-axis
• Assuming axis direction stays the same
• Believing invert_xaxis() causes error

4. Identify the error in this code that tries to invert the y-axis:

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([1, 2, 3], [10, 20, 30])
plt.invert_yaxis()
plt.show()

medium

A. invert_yaxis() should be called on ax, not plt.

B. invert_yaxis() does not exist in matplotlib.

C. The plot function is missing axis inversion parameter.

D. plt.show() must be called before invert_yaxis().

Solution

1. Step 1: Check where invert_yaxis() is called

   The code calls invert_yaxis() on plt, which is incorrect.

2. Step 2: Correct usage of invert_yaxis()

   This method must be called on the axis object ax, not on the pyplot module plt.

3. Final Answer:

   invert_yaxis() should be called on ax, not plt. -> Option A

4. Quick Check:

   Call invert_yaxis() on ax object [OK]

Hint: Call invert_yaxis() on ax, not plt [OK]

Common Mistakes:

• Calling invert_yaxis() on plt instead of ax
• Assuming invert_yaxis() is a plt method
• Calling plt.show() before inversion

5. You want to plot temperature decreasing over time, but your data has time increasing left to right. How can you use inverted axes to show time decreasing from left to right and temperature increasing bottom to top? Choose the correct code snippet.

hard

A. ax.plot(time, temperature)
ax.invert_xaxis()
ax.invert_yaxis()

B. ax.plot(time, temperature)
ax.invert_xaxis()

C. ax.plot(time, temperature)
ax.invert_yaxis()

D. ax.plot(time, temperature)

Solution

1. Step 1: Understand the desired axis directions

   Time should decrease from left to right, so x-axis must be inverted. Temperature should increase bottom to top, so y-axis stays normal.

2. Step 2: Choose the correct inversion method

   Only ax.invert_xaxis() is needed to flip time axis; inverting y-axis would reverse temperature direction incorrectly.

3. Final Answer:

   ax.plot(time, temperature) ax.invert_xaxis() -> Option B

4. Quick Check:

   Invert x-axis only to reverse time direction [OK]

Hint: Invert only the axis that needs reversed direction [OK]

Common Mistakes:

• Inverting both axes unnecessarily
• Not inverting any axis
• Inverting y-axis instead of x-axis