Broken axes concept in Matplotlib - Step-by-Step Execution

Concept Flow - Broken axes concept

Start: Prepare data

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Create figure and axes

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Plot data on first axis

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Plot data on second axis

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Hide spines and ticks between axes

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Add diagonal lines to show break

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Show combined plot with broken axes

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End

This flow shows how to create a plot with broken axes by preparing data, plotting on two axes, hiding the break area, and adding diagonal lines to indicate the break.

Execution Sample

Matplotlib

import matplotlib.pyplot as plt
fig, (ax1, ax2) = plt.subplots(1, 2, sharey=True)
ax1.plot([1, 2, 3], [10, 20, 30])
ax2.plot([1, 2, 3], [100, 200, 300])
plt.show()

This code creates two side-by-side plots sharing the y-axis to simulate broken axes.

Execution Table

Step	Action	Axes State	Plot Data	Visual Result
1	Import matplotlib.pyplot as plt	No axes created	No data plotted	No plot yet
2	Create figure and two subplots sharing y-axis	Two axes: ax1 and ax2 created side by side	No data plotted	Empty figure with two axes
3	Plot data [10,20,30] on ax1	ax1 ready	Line plot on ax1 with y=[10,20,30]	Left plot shows small y values
4	Plot data [100,200,300] on ax2	ax2 ready	Line plot on ax2 with y=[100,200,300]	Right plot shows large y values
5	Hide spines and ticks between ax1 and ax2	Axes spines adjusted	No new data	Gap between plots looks like broken axis
6	Add diagonal lines on break	Decorations added	No new data	Visual break lines appear between axes
7	Show plot	Final state	Both plots visible	Combined plot with broken y-axis shown
8	End	Plot window open	Data displayed	User sees broken axes plot

💡 Plot displayed with two axes showing different y ranges to simulate broken axes.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	Final
fig	None	Figure object created	Figure unchanged	Figure unchanged	Figure unchanged	Figure unchanged	Figure unchanged
ax1	None	Axes object created	Line plotted with y=[10,20,30]	Line plotted	Spines hidden on right	Diagonal lines added	Final broken axes left plot
ax2	None	Axes object created	No plot	Line plotted with y=[100,200,300]	Spines hidden on left	Diagonal lines added	Final broken axes right plot

Key Moments - 3 Insights

Why do we create two separate axes instead of one?

We create two axes to show different y-axis ranges side by side, which simulates a broken axis effect. This is shown in execution_table steps 2, 3, and 4 where each axis plots different y data.

How do diagonal lines indicate the axis break?

Diagonal lines are drawn between the two axes to visually signal the break in the axis scale. This is done after hiding spines (step 6) and helps users understand the axis is discontinuous.

Why do we share the y-axis between the two plots?

Sharing the y-axis aligns the two plots vertically so the broken axis looks continuous except for the break. This is set in step 2 with sharey=True.

Visual Quiz - 3 Questions

Look at the execution table at step 4. What data is plotted on ax2?

A [10, 20, 30]

B [100, 200, 300]

C [1, 2, 3]

D No data plotted yet

💡 Hint

Check the 'Plot Data' column in row for step 4 in execution_table.

At which step do we add diagonal lines to show the axis break?

A Step 6

B Step 5

C Step 3

D Step 7

💡 Hint

Look at the 'Action' column for the step mentioning diagonal lines in execution_table.

If we do not share the y-axis (remove sharey=True), what changes in the plot?

A Plots will merge into one

B Diagonal lines will not appear

C Axes will not align vertically, making the broken axis effect less clear

D Data will not plot

💡 Hint

Refer to key_moments about why sharey=True is used.

Concept Snapshot

Broken axes concept in matplotlib:
- Create two subplots side by side with sharey=True
- Plot different y ranges on each axis
- Hide spines and ticks between axes
- Add diagonal lines to indicate axis break
- Show combined plot simulating a broken axis

Full Transcript

This visual execution shows how to create a broken axes plot in matplotlib. First, we import matplotlib and create a figure with two subplots side by side sharing the y-axis. We plot smaller y values on the left axis and larger y values on the right axis. Then, we hide the spines and ticks between the two axes to create a visual gap. Diagonal lines are added between the axes to indicate the break in the axis scale. Finally, the combined plot is shown, allowing viewers to see data with a discontinuous y-axis. This technique helps display data with very different scales clearly.

Practice

1. What is the main purpose of using broken axes in matplotlib plots?

easy

A. To skip unimportant data ranges and focus on key parts

B. To add 3D effects to the plot

C. To change the color scheme automatically

D. To animate the plot over time

Solution

1. Step 1: Understand the concept of broken axes

   Broken axes are used to skip over parts of the axis where data is not important or has large gaps.

2. Step 2: Identify the main purpose

   This helps to focus on important data ranges without showing the entire axis continuously.

3. Final Answer:

   To skip unimportant data ranges and focus on key parts -> Option A

4. Quick Check:

   Broken axes = skip gaps [OK]

Hint: Broken axes hide gaps to highlight important data [OK]

Common Mistakes:

• Thinking broken axes add 3D or animation
• Confusing broken axes with color changes
• Assuming broken axes zoom in automatically

2. Which of the following is the correct way to import the brokenaxes package to use brokenaxes(...) directly for creating broken axes plots?

easy

A. from brokenaxes import BrokenAxes

B. import brokenaxes as ba

C. from brokenaxes import brokenaxes

D. import matplotlib.brokenaxes as ba

Solution

1. Step 1: Recall the correct import syntax

   The brokenaxes package provides the brokenaxes function to create broken axes plots.

2. Step 2: Identify the correct import statement

   The correct way is from brokenaxes import brokenaxes to access the function directly.

3. Final Answer:

   from brokenaxes import brokenaxes -> Option C

4. Quick Check:

   Import brokenaxes function = from brokenaxes import brokenaxes [OK]

Hint: Import brokenaxes function directly from brokenaxes [OK]

Common Mistakes:

• Using capital 'BrokenAxes' instead of 'brokenaxes'
• Trying to import from matplotlib instead of brokenaxes
• Using wrong import syntax causing ImportError

3. What will the following code output?

from brokenaxes import brokenaxes
import matplotlib.pyplot as plt

bax = brokenaxes(ylims=((0, 2), (8, 10)))
bax.plot([0, 1, 2, 3], [1, 1.5, 9, 9.5])
plt.show()

medium

A. A plot with y-axis broken between 2 and 8 showing points near 1 and 9

B. A plot with continuous y-axis from 0 to 10

C. An error because ylims must be a single tuple

D. A plot with x-axis broken between 2 and 8

Solution

1. Step 1: Analyze the ylims parameter

   The ylims=((0, 2), (8, 10)) means the y-axis is broken to show two ranges: 0 to 2 and 8 to 10, skipping 2 to 8.

2. Step 2: Understand the plotted points

   The y-values are 1, 1.5, 9, and 9.5, which fit into the two visible y-axis ranges.

3. Final Answer:

   A plot with y-axis broken between 2 and 8 showing points near 1 and 9 -> Option A

4. Quick Check:

   ylims tuple of ranges = broken y-axis [OK]

Hint: ylims with tuples creates breaks on y-axis [OK]

Common Mistakes:

• Assuming y-axis is continuous without breaks
• Confusing x-axis and y-axis breaks
• Expecting an error from tuple ylims

4. Identify the error in this code snippet that tries to create broken axes:

from brokenaxes import brokenaxes
import matplotlib.pyplot as plt

bax = brokenaxes(xlims=(0, 2), (5, 7))
bax.plot([1, 6], [10, 20])
plt.show()

medium

A. plt.show() must be called before plot

B. plot function requires x and y to be the same length

C. BrokenAxes cannot be used with xlims parameter

D. xlims should be a tuple of tuples, not separate tuples

Solution

1. Step 1: Check the xlims argument syntax

   The code uses xlims=(0, 2), (5, 7) which is invalid syntax; it should be a single tuple containing tuples like xlims=((0, 2), (5, 7)).

2. Step 2: Confirm other parts are correct

   The plot call and plt.show() are correct; the error is only in xlims syntax.

3. Final Answer:

   xlims should be a tuple of tuples, not separate tuples -> Option D

4. Quick Check:

   xlims syntax = tuple of tuples [OK]

Hint: Use double parentheses for xlims tuple of ranges [OK]

Common Mistakes:

• Passing multiple tuples without enclosing in one tuple
• Mixing up xlims and ylims syntax
• Calling plt.show() too early

5. You have data with y-values clustered around 0-3 and 50-55, with a large gap in between. How would you create a broken y-axis to show both clusters clearly using brokenaxes?

hard

A. Plot two separate figures for each cluster

B. Use ylims=((0, 3), (50, 55)) when creating brokenaxes

C. Use xlims=((0, 3), (50, 55)) to break x-axis instead

D. Use ylims=(0, 55) to show full range without breaks

Solution

1. Step 1: Identify the axis to break

   The gap is in y-values, so the y-axis needs to be broken to skip the large gap between 3 and 50.

2. Step 2: Set ylims with two ranges

   Using ylims=((0, 3), (50, 55)) creates a broken y-axis showing both clusters clearly.

3. Final Answer:

   Use ylims=((0, 3), (50, 55)) when creating brokenaxes -> Option B

4. Quick Check:

   Broken y-axis = ylims tuple of ranges [OK]

Hint: Set ylims with two ranges to break y-axis gaps [OK]

Common Mistakes:

• Breaking x-axis instead of y-axis
• Using single continuous ylims hiding gap
• Plotting separate figures unnecessarily