Lollipop charts in Matplotlib - Step-by-Step Execution

Concept Flow - Lollipop charts

Start with data points

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Plot baseline axis

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Draw vertical lines from baseline to each data point

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Draw dots at data points

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Add labels and style

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Display lollipop chart

The flow starts with data, draws lines from a baseline to each point, then adds dots on top to create a lollipop chart.

Execution Sample

Matplotlib

import matplotlib.pyplot as plt

x = [1, 2, 3, 4]
y = [10, 15, 7, 12]

plt.stem(x, y, basefmt=" ")
plt.show()

This code creates a simple lollipop chart with vertical lines and dots for each data point.

Execution Table

Step	Action	Data/Variables	Plot Elements Created	Result
1	Define x and y data	x=[1,2,3,4], y=[10,15,7,12]	None	Data ready for plotting
2	Call plt.stem(x, y, basefmt=" ")	x, y	Vertical lines from y=0 to y[i] at x[i], dots at (x[i], y[i])	Lollipop chart elements created
3	Render plot with plt.show()	Plot elements	Figure window opens	Lollipop chart displayed
4	User views chart	Visual output	Lines and dots visible	Chart shows data points clearly

💡 Plot displayed and program waits for user to close window

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
x	undefined	[1, 2, 3, 4]	[1, 2, 3, 4]	[1, 2, 3, 4]
y	undefined	[10, 15, 7, 12]	[10, 15, 7, 12]	[10, 15, 7, 12]

Key Moments - 2 Insights

Why do we use plt.stem instead of plt.plot for lollipop charts?

plt.stem automatically draws vertical lines from the baseline to each data point and places dots, matching the lollipop chart style, as shown in execution_table step 2.

What does basefmt=" " do in plt.stem?

It removes the baseline line at y=0 so only the vertical lines and dots appear, making the chart cleaner, as seen in the plot elements created in step 2.

Visual Quiz - 3 Questions

Look at the execution_table step 2, what plot elements are created by plt.stem?

A Only dots at data points

B Vertical lines from baseline to data points and dots at data points

C Only vertical lines without dots

D A line connecting all data points

💡 Hint

See 'Plot Elements Created' column in execution_table step 2

According to variable_tracker, what is the value of y after step 1?

A [1, 2, 3, 4]

B undefined

C [10, 15, 7, 12]

D None

💡 Hint

Check the 'After Step 1' column for variable y in variable_tracker

If we remove basefmt=" " from plt.stem, what changes in the plot?

A Baseline line at y=0 appears

B Vertical lines disappear

C Dots disappear

D Plot does not display

💡 Hint

Refer to key_moments explanation about basefmt in plt.stem

Concept Snapshot

Lollipop charts use vertical lines from a baseline to data points with dots on top.
Use matplotlib's plt.stem(x, y, basefmt=" ") to create them.
basefmt=" " hides the baseline line for clarity.
They highlight individual values clearly like lollipops on sticks.

Full Transcript

Lollipop charts show data points with vertical lines from a baseline and dots on top. We start by defining x and y data arrays. Then we use matplotlib's plt.stem function to draw vertical lines from zero to each y value at x positions, and place dots at those points. The basefmt=" " argument removes the baseline line for a cleaner look. Finally, plt.show() displays the chart. This method visually emphasizes each data point individually, making it easy to compare values. The execution table traces these steps, showing data preparation, plot element creation, and display. Variable tracker confirms data values remain unchanged. Key moments clarify why plt.stem is used and the role of basefmt. The visual quiz tests understanding of plot elements, variable states, and formatting effects.