Diverging bar charts in Matplotlib - Step-by-Step Execution

Concept Flow - Diverging bar charts

Prepare data with positive and negative values

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Sort or order data if needed

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Assign colors based on value sign

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Plot horizontal bars with lengths = values

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Add labels and title

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Display chart with diverging bars

This flow shows how to create a diverging bar chart by preparing data, assigning colors based on positive or negative values, plotting bars, and displaying the chart.

Execution Sample

Matplotlib

import matplotlib.pyplot as plt
values = [20, -15, 30, -10, 5]
colors = ['green' if v >= 0 else 'red' for v in values]
plt.barh(range(len(values)), values, color=colors)
plt.show()

This code plots a horizontal bar chart with bars colored green for positive and red for negative values.

Execution Table

Step	Action	Variable/Value	Result/Effect
1	Define values list	values = [20, -15, 30, -10, 5]	List with positive and negative numbers created
2	Assign colors based on sign	colors = ['green' if v >= 0 else 'red' for v in values]	colors = ['green', 'red', 'green', 'red', 'green']
3	Call plt.barh with values and colors	plt.barh(range(5), values, color=colors)	Horizontal bars plotted with correct colors
4	Call plt.show()	plt.show()	Chart window opens showing diverging bar chart
5	End	-	Execution stops after displaying chart

💡 Chart displayed and script ends

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
values	undefined	[20, -15, 30, -10, 5]	[20, -15, 30, -10, 5]	[20, -15, 30, -10, 5]
colors	undefined	undefined	['green', 'red', 'green', 'red', 'green']	['green', 'red', 'green', 'red', 'green']

Key Moments - 2 Insights

Why do some bars appear in red and others in green?

Bars are colored based on whether their values are negative or positive, as shown in step 2 of the execution table where colors are assigned conditionally.

What does plt.barh(range(len(values)), values, color=colors) do exactly?

It plots horizontal bars at positions 0 to 4 with lengths from values and colors from the colors list, as explained in step 3 of the execution table.

Visual Quiz - 3 Questions

Look at the execution table, what is the color assigned to the value -10 at step 2?

A blue

B green

C red

D yellow

💡 Hint

Check the colors list in step 2 of the execution table where negative values get 'red'.

At which step does the chart actually get displayed?

A Step 1

B Step 4

C Step 3

D Step 5

💡 Hint

Look at the action in step 4 where plt.show() is called.

If the values list was all positive, how would the colors list change at step 2?

A All colors would be 'green'

B All colors would be 'red'

C Colors would alternate between 'green' and 'red'

D Colors would be empty

💡 Hint

Refer to the color assignment rule in step 2: positive values get 'green'.

Concept Snapshot

Diverging bar charts show positive and negative values with bars going right or left.
Use plt.barh() for horizontal bars.
Assign colors based on sign: green for positive, red for negative.
Plot bars with lengths = values and colors assigned.
Add labels and show chart with plt.show().

Full Transcript

This visual execution traces how to create a diverging bar chart using matplotlib in Python. First, a list of values with positive and negative numbers is defined. Then, colors are assigned to each value: green if the value is positive or zero, red if negative. Next, plt.barh() plots horizontal bars at positions 0 to 4 with lengths equal to the values and colors assigned accordingly. Finally, plt.show() displays the chart window with the diverging bars. The execution table shows each step and variable changes, helping beginners understand how the chart is built step-by-step.