Violin plot with plt.violinplot in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of basic violin plot code

What will be the output of this code snippet that creates a violin plot for two groups of data?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np

data1 = np.random.normal(0, 1, 100)
data2 = np.random.normal(5, 1, 100)

plt.violinplot([data1, data2])
plt.show()

A A plot with two violin shapes side by side, one centered near 0 and the other near 5 on the y-axis.

B A bar chart showing the mean values of data1 and data2.

C A scatter plot of all points from data1 and data2.

D An error because plt.violinplot requires data as a single array, not a list.

💡 Hint

Think about what plt.violinplot does with a list of arrays.

plt.violinplot can take a list of datasets and draws a violin plot for each dataset side by side. Here, data1 is centered near 0 and data2 near 5, so the violins appear at those positions.

❓ data_output

intermediate

Number of violins plotted

Given this code, how many violins will appear in the plot?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np

np.random.seed(0)
data = [np.random.normal(loc, 1, 50) for loc in range(4)]
plt.violinplot(data)
plt.show()

A 3

B 1

C 4

D 0

💡 Hint

Count how many datasets are in the list passed to plt.violinplot.

The list 'data' contains 4 arrays, so plt.violinplot draws 4 violins, one for each dataset.

🔧 Debug

advanced

Identify the error in violin plot code

What error will this code produce when run?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np

data = np.random.normal(0, 1, 100)
plt.violinplot(data, positions=[1, 2])
plt.show()

A TypeError: data must be a list of arrays

B ValueError: positions length does not match number of datasets

C No error, plot shows one violin at position 1 and another at 2

D IndexError: positions index out of range

💡 Hint

Check if the number of positions matches the number of datasets.

The data is a single array, so plt.violinplot expects one position. Providing two positions causes a ValueError due to mismatch.

❓ visualization

advanced

Effect of bandwidth parameter on violin plot

Which option best describes the effect of setting the 'bw_method' parameter in plt.violinplot?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np

data = np.random.normal(0, 1, 100)
plt.violinplot(data, bw_method=0.1)
plt.show()

A A violin plot with more detailed peaks and valleys showing fine distribution features

B An error because bw_method is not a valid parameter

C No visible change compared to default bandwidth

D A smoother violin shape with less detail in the distribution

💡 Hint

Lower bandwidth means the kernel density estimate is more sensitive to data variations.

Lower bw_method values make the kernel density estimate more sensitive, showing more detailed distribution shapes in the violin plot.

🧠 Conceptual

expert

Understanding violin plot components

Which statement correctly describes the components shown in a violin plot created by plt.violinplot?

A It plots individual data points as dots without any distribution shape.

B It only shows the median and mean values as points without distribution shape.

C It displays a box plot inside a histogram for each dataset.

D It shows the data distribution as a kernel density estimate mirrored on both sides, with optional markers for median and quartiles.

💡 Hint

Think about how violin plots combine density and summary statistics.

Violin plots show the kernel density estimate mirrored to form a shape, and can include markers for median and quartiles to summarize data.