Unequal subplot sizes in Matplotlib - Step-by-Step Execution

Concept Flow - Unequal subplot sizes

Start: Create Figure

↓

Define GridSpec with unequal ratios

↓

Add subplot 1 with larger size

↓

Add subplot 2 with smaller size

↓

Plot data on each subplot

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Show figure with unequal subplot sizes

We create a figure, define a grid layout with different size ratios, add subplots accordingly, plot data, and display the figure.

Execution Sample

Matplotlib

import matplotlib.pyplot as plt
import matplotlib.gridspec as gridspec

fig = plt.figure()
gs = gridspec.GridSpec(1, 2, width_ratios=[3, 1])
ax1 = fig.add_subplot(gs[0, 0])
ax2 = fig.add_subplot(gs[0, 1])
ax1.plot([1,2,3], [1,4,9])
ax2.plot([1,2,3], [1,2,3])
plt.show()

This code creates two subplots side by side with the first subplot three times wider than the second.

Execution Table

Step	Action	Object Created	Size/Ratio	Plot Data	Output
1	Create figure	Figure	Full canvas	None	Figure object ready
2	Define GridSpec	GridSpec	1 row, 2 cols, width_ratios=[3,1]	None	Grid layout set
3	Add subplot ax1	AxesSubplot ax1	Width ratio 3 units	Plot y=x^2	Left large subplot created
4	Add subplot ax2	AxesSubplot ax2	Width ratio 1 unit	Plot y=x	Right smaller subplot created
5	Display figure	Figure with 2 subplots	Unequal widths	Both plots visible	Figure shown on screen

💡 All steps complete, figure displayed with unequal subplot sizes.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
fig	None	Figure object created	Figure with GridSpec	Figure with 2 subplots	Figure ready to show
gs	None	GridSpec with ratios [3,1]	GridSpec unchanged	GridSpec unchanged	GridSpec unchanged
ax1	None	None	AxesSubplot with width ratio 3	AxesSubplot with width ratio 3	AxesSubplot ready
ax2	None	None	None	AxesSubplot with width ratio 1	AxesSubplot ready

Key Moments - 3 Insights

Why does the first subplot appear wider than the second?

Because the GridSpec was defined with width_ratios=[3,1], the first subplot gets 3 parts width and the second gets 1 part, making the first subplot three times wider (see execution_table step 2 and 3).

What happens if we change width_ratios to [1,3]?

The second subplot becomes wider than the first, reversing their sizes. This is controlled by the width_ratios parameter in GridSpec (see variable_tracker gs after step 2).

Can we have unequal heights instead of widths?

Yes, by using height_ratios in GridSpec for rows instead of width_ratios for columns, you can control vertical sizes similarly.

Visual Quiz - 3 Questions

Look at the execution_table at step 3. What is the width ratio of subplot ax1?

A 1 unit

B 3 units

C Equal width

D Undefined

💡 Hint

Check the 'Size/Ratio' column in execution_table row for step 3.

At which step is the second subplot (ax2) created?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Look at the 'Action' column in execution_table for when ax2 is added.

If width_ratios were changed to [1, 3], how would the subplot sizes change?

A Both subplots become equal size

B First subplot becomes larger, second smaller

C First subplot becomes smaller, second larger

D No change in sizes

💡 Hint

Refer to key_moments explanation about width_ratios effect on subplot sizes.

Concept Snapshot

Use matplotlib.gridspec.GridSpec to create subplots with unequal sizes.
Define width_ratios or height_ratios to control relative sizes.
Add subplots using the GridSpec slices.
Plot data on each subplot.
Call plt.show() to display the figure with unequal subplot sizes.

Full Transcript

This visual execution shows how to create subplots with unequal sizes using matplotlib's GridSpec. First, a figure is created. Then, GridSpec defines a grid layout with specified width ratios, here [3,1], meaning the first subplot is three times wider than the second. Subplots are added according to this grid. Data is plotted on each subplot. Finally, the figure is displayed showing the unequal subplot sizes clearly. Variables like fig, gs, ax1, and ax2 change step-by-step as subplots are created and plotted. Key moments clarify why the first subplot is wider and how changing width_ratios affects sizes. The quiz tests understanding of these steps and ratios.

Practice

1. What is the main advantage of using unequal subplot sizes in matplotlib?

easy

A. To automatically adjust colors of the plots

B. To make all charts the same size for uniformity

C. To highlight important charts by giving them more space

D. To reduce the total number of charts displayed

Solution

1. Step 1: Understand subplot size purpose

   Unequal subplot sizes allow some plots to be larger, drawing more attention.

2. Step 2: Compare options

   Only To highlight important charts by giving them more space mentions highlighting important charts by size, which is the main advantage.

3. Final Answer:

   To highlight important charts by giving them more space -> Option C

4. Quick Check:

   Unequal sizes highlight key charts [OK]

Hint: Unequal sizes = emphasize important plots [OK]

Common Mistakes:

• Thinking all subplots must be equal size
• Confusing size with color or number of plots
• Assuming unequal sizes reduce charts

2. Which of the following is the correct way to create subplots with unequal sizes using gridspec_kw in plt.subplots()?

easy

A. plt.subplots(1, 2, gridspec_kw={'width_ratios': [2, 1]})

B. plt.subplots(2, 1, gridspec_kw={'height_ratios': [1, 2]})

C. plt.subplots(1, 2, gridspec_kw={'height_ratios': [2, 1]})

D. plt.subplots(2, 1, gridspec_kw={'width_ratios': [1, 2]})

Solution

1. Step 1: Identify correct parameter for horizontal subplots

   For 1 row and 2 columns, use 'width_ratios' to set horizontal size ratios.

2. Step 2: Match ratios to subplot layout

   plt.subplots(1, 2, gridspec_kw={'width_ratios': [2, 1]}) uses 1 row, 2 columns with width_ratios, which is correct syntax.

3. Final Answer:

   plt.subplots(1, 2, gridspec_kw={'width_ratios': [2, 1]}) -> Option A

4. Quick Check:

   Width ratios for columns = plt.subplots(1, 2, gridspec_kw={'width_ratios': [2, 1]}) [OK]

Hint: Use width_ratios for columns, height_ratios for rows [OK]

Common Mistakes:

• Mixing width_ratios with rows instead of columns
• Using height_ratios for horizontal layout
• Wrong number of rows and columns in function

3. What will be the width ratio of the two subplots created by this code?

fig, axs = plt.subplots(1, 2, gridspec_kw={'width_ratios': [3, 1]})

medium

A. Both subplots have equal width

B. The subplots have random widths

C. The second subplot is 3 times wider than the first

D. The first subplot is 3 times wider than the second

Solution

1. Step 1: Understand width_ratios parameter

   The list [3, 1] means the first subplot width is 3 units, second is 1 unit.

2. Step 2: Interpret ratio meaning

   This means the first subplot is 3 times wider than the second subplot.

3. Final Answer:

   The first subplot is 3 times wider than the second -> Option D

4. Quick Check:

   Width ratio 3:1 means first is 3x wider [OK]

Hint: Ratio list directly shows relative sizes [OK]

Common Mistakes:

• Assuming equal widths despite ratios
• Reversing which subplot is wider
• Ignoring the ratio values

4. Identify the error in this code that tries to create unequal subplot sizes:

fig, axs = plt.subplots(2, 1, gridspec_kw={'width_ratios': [1, 2]})

medium

A. Incorrect number of subplots specified

B. Using width_ratios for vertical subplots instead of height_ratios

C. Missing plt.show() to display plots

D. width_ratios list length does not match subplot count

Solution

1. Step 1: Check subplot layout

   2 rows and 1 column means vertical stacking of subplots.

2. Step 2: Verify correct ratio parameter

   For vertical layout, use 'height_ratios', not 'width_ratios'.

3. Final Answer:

   Using width_ratios for vertical subplots instead of height_ratios -> Option B

4. Quick Check:

   Vertical layout needs height_ratios [OK]

Hint: Use height_ratios for rows, width_ratios for columns [OK]

Common Mistakes:

• Confusing width_ratios and height_ratios
• Ignoring subplot grid shape
• Assuming plt.show() affects subplot sizes

5. You want to create a figure with 3 subplots in one row where the middle subplot is twice as wide as the others. Which code correctly achieves this?

hard

A. plt.subplots(1, 3, gridspec_kw={'width_ratios': [1, 2, 1]})

B. plt.subplots(3, 1, gridspec_kw={'height_ratios': [1, 2, 1]})

C. plt.subplots(1, 3, gridspec_kw={'height_ratios': [1, 2, 1]})

D. plt.subplots(3, 1, gridspec_kw={'width_ratios': [1, 2, 1]})

Solution

1. Step 1: Determine subplot layout

   One row and three columns means horizontal layout.

2. Step 2: Choose correct ratio parameter

   For horizontal layout, use 'width_ratios' to set widths.

3. Step 3: Set ratios to make middle subplot twice as wide

   Use [1, 2, 1] so middle subplot is twice the width of others.

4. Final Answer:

   plt.subplots(1, 3, gridspec_kw={'width_ratios': [1, 2, 1]}) -> Option A

5. Quick Check:

   Horizontal layout with width_ratios = plt.subplots(1, 3, gridspec_kw={'width_ratios': [1, 2, 1]}) [OK]

Hint: Middle subplot twice wide = width_ratios [1, 2, 1] [OK]

Common Mistakes:

• Using height_ratios for horizontal layout
• Setting wrong number of rows and columns
• Reversing ratio order