Lollipop charts in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a basic lollipop chart code

What will be the output of this Python code that creates a lollipop chart using matplotlib?

Matplotlib

import matplotlib.pyplot as plt

categories = ['A', 'B', 'C', 'D']
values = [4, 7, 1, 8]

plt.stem(categories, values, basefmt=" ", use_line_collection=True)
plt.show()

A A vertical lollipop chart with stems from zero to values for categories A, B, C, D

B A horizontal bar chart with bars for categories A, B, C, D

C A scatter plot with points at (categories, values) but no stems

D A line plot connecting points for categories A, B, C, D

💡 Hint

Look at the plt.stem function and what it draws.

The plt.stem function creates vertical lines (stems) from a baseline to the data points, with markers at the data points, forming a lollipop chart.

❓ data_output

intermediate

Number of stems in a lollipop chart

Given this code, how many stems (lines) will the lollipop chart display?

Matplotlib

import matplotlib.pyplot as plt

labels = ['X', 'Y', 'Z']
values = [10, 5, 15]

plt.stem(labels, values, basefmt=" ", use_line_collection=True)
plt.show()

A 1

B 0

C 3

D 15

💡 Hint

Count how many data points are plotted.

Each data point corresponds to one stem line in the lollipop chart, so the number of stems equals the number of values.

🔧 Debug

advanced

Identify the error in lollipop chart code

What error will this code raise when run?

Matplotlib

import matplotlib.pyplot as plt

categories = ['A', 'B', 'C']
values = [5, 10]

plt.stem(categories, values, basefmt=" ", use_line_collection=True)
plt.show()

A No error, chart displays correctly

B TypeError: categories must be numeric

C SyntaxError: invalid syntax

D ValueError: x and y must have same length

💡 Hint

Check if the lengths of categories and values match.

The plt.stem function requires x and y to have the same length. Here categories has 3 items but values has 2, causing a ValueError.

❓ visualization

advanced

Effect of changing baseline in lollipop chart

What will be the visual effect of setting basefmt='r-' in plt.stem for this code?

Matplotlib

import matplotlib.pyplot as plt

labels = ['P', 'Q', 'R']
values = [3, 6, 9]

plt.stem(labels, values, basefmt='r-', use_line_collection=True)
plt.show()

A The baseline line will be red and solid under the stems

B The stems will be red instead of default color

C The markers at data points will be red circles

D The chart will have no baseline line visible

💡 Hint

basefmt controls the baseline line style and color.

The basefmt parameter sets the style of the baseline line. 'r-' means a red solid line under the stems.

🚀 Application

expert

Choosing correct code for horizontal lollipop chart

Which option produces a horizontal lollipop chart with categories on y-axis and values on x-axis?

A

plt.stem(labels, values, basefmt=' ', use_line_collection=True)
plt.gca().invert_yaxis()
plt.show()

B

plt.stem(values, labels, basefmt=' ', orientation='horizontal', use_line_collection=True)
plt.show()

C

plt.stem(values, labels, basefmt=' ', use_line_collection=True)
plt.show()

D

plt.stem(labels, values, basefmt=' ', orientation='horizontal', use_line_collection=True)
plt.show()

💡 Hint

Check the orientation parameter and axis order for horizontal stem plots.

To create a horizontal lollipop chart, plt.stem must have orientation='horizontal' and x, y data swapped: x=values, y=labels. Option B correctly sets orientation and axis order.