Figure and axes creation in Data Analysis Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a figure in data visualization?

A figure is the entire window or page that holds one or more plots or charts. Think of it as a blank canvas where you draw your graphs.

beginner

What is an axes in a figure?

Axes are the parts of the figure where the actual data is plotted. It includes the x-axis, y-axis, and the area where the graph appears.

beginner

How do you create a figure and axes using Matplotlib in Python?

Use the command fig, ax = plt.subplots(). This creates a figure and a single axes inside it, ready for plotting.

intermediate

Why might you want to create multiple axes in one figure?

To show multiple plots side by side or in a grid, making it easier to compare data visually in one window.

beginner

What does the figsize parameter control when creating a figure?

It sets the size of the figure in inches, controlling how big or small the whole plot area will be.

Which command creates a figure and axes in Matplotlib?

A fig, ax = plt.subplots()

B plt.create_figure()

C axes = plt.figure()

D plot.figure()

The correct command is fig, ax = plt.subplots() which creates both figure and axes.

What does an axes object represent?

A The entire plotting window

B The area where data is plotted including axes lines

C Only the x-axis line

D The title of the plot

Axes is the area inside the figure where the data is drawn, including x and y axes.

How can you create multiple plots in one figure?

A By calling plt.plot() multiple times

B By using plt.figure() multiple times

C By creating multiple axes using plt.subplots() with rows and columns

D By changing the figure size

Using plt.subplots(nrows, ncols) creates multiple axes in one figure.

What does the figsize parameter control?

A The size of the figure in inches

B The number of axes

C The font size of labels

D The color of the plot

Figsize sets the width and height of the figure in inches.

If you want a single plot, which is the simplest way to create figure and axes?

A plt.axes() only

B plt.figure() only

C plt.plot() only

D fig, ax = plt.subplots()

Using plt.subplots() creates both figure and axes in one step.

Explain the difference between a figure and axes in data visualization.

Think of a figure as a page and axes as the drawing area on that page.

Describe how to create multiple plots in one figure using Python's Matplotlib.

Consider how you might arrange photos in a photo album.

Practice

1. What does the plt.subplots() function return in matplotlib?

easy

A. A figure and one or more axes objects

B. Only a figure object

C. Only an axes object

D. A list of data points

Solution

1. Step 1: Understand plt.subplots() purpose

   The function is designed to create a figure and axes together for plotting.

2. Step 2: Check the return values

   It returns a tuple: the first is the figure, the second is the axes (single or array).

3. Final Answer:

   A figure and one or more axes objects -> Option A

4. Quick Check:

   plt.subplots() = (figure, axes) [OK]

Hint: Remember plt.subplots() returns figure and axes together [OK]

Common Mistakes:

• Thinking it returns only figure or only axes
• Confusing axes with data points
• Assuming it returns a plot directly

2. Which of the following is the correct syntax to create a figure with 2 rows and 3 columns of axes using matplotlib?

easy

A. fig, axes = plt.subplots(rows=3, cols=2)

B. fig, axes = plt.subplots(2, 3)

C. fig, axes = plt.subplots(3, 2)

D. fig, axes = plt.subplots(2*3)

Solution

1. Step 1: Recall plt.subplots() parameters

   The first argument is number of rows, the second is number of columns.

2. Step 2: Match the correct order

   To create 2 rows and 3 columns, use plt.subplots(2, 3).

3. Final Answer:

   fig, axes = plt.subplots(2, 3) -> Option B

4. Quick Check:

   Rows first, columns second in plt.subplots() [OK]

Hint: Remember rows first, columns second in plt.subplots() [OK]

Common Mistakes:

• Swapping rows and columns order
• Using keyword arguments incorrectly
• Passing a single number instead of two

3. What will be the shape of axes when running fig, axes = plt.subplots(2, 2)?

medium

A. A 2x2 numpy array of AxesSubplot objects

B. A list of 4 AxesSubplot objects

C. A single AxesSubplot object

D. A dictionary of axes objects

Solution

1. Step 1: Understand axes structure for multiple subplots

   When more than one subplot is created, axes is a 2D array matching the grid shape.

2. Step 2: Check the shape for 2 rows and 2 columns

   Axes will be a 2x2 numpy array of AxesSubplot objects.

3. Final Answer:

   A 2x2 numpy array of AxesSubplot objects -> Option A

4. Quick Check:

   Multiple subplots = axes array matching grid [OK]

Hint: Multiple subplots return axes array matching rows and columns [OK]

Common Mistakes:

• Expecting a flat list instead of 2D array
• Thinking axes is a single object always
• Confusing axes with figure

4. Identify the error in this code snippet:

fig, ax = plt.subplots(2, 2)
ax.plot([1, 2, 3], [4, 5, 6])

medium

A. fig and ax are swapped in assignment

B. plt.subplots() cannot create 2x2 axes

C. ax is an array, so ax.plot() causes an error

D. The plot data lists have different lengths

Solution

1. Step 1: Check the shape of ax from plt.subplots(2, 2)

   ax is a 2x2 array of axes, not a single axes object.

2. Step 2: Understand why ax.plot() fails

   Calling plot() on an array causes an AttributeError because arrays don't have plot method.

3. Final Answer:

   ax is an array, so ax.plot() causes an error -> Option C

4. Quick Check:

   Array of axes needs indexing before plot() [OK]

Hint: Index axes array before plotting when multiple subplots exist [OK]

Common Mistakes:

• Trying to plot on axes array directly
• Assuming plt.subplots(2,2) returns single axes
• Ignoring need to index axes for plotting

5. You want to create a figure with 3 subplots stacked vertically and set the figure size to 8 inches wide and 12 inches tall. Which code correctly does this?

hard

A. fig, axes = plt.subplots(1, 3, figsize=(12, 8))

B. fig, axes = plt.subplots(3, figsize=(8, 12))

C. fig, axes = plt.subplots(3, 1, size=(8, 12))

D. fig, axes = plt.subplots(3, 1, figsize=(8, 12))

Solution

1. Step 1: Determine subplot layout for vertical stacking

   3 subplots stacked vertically means 3 rows and 1 column.

2. Step 2: Set figure size correctly

   Use figsize=(width, height) with width=8 and height=12 inches.

3. Final Answer:

   fig, axes = plt.subplots(3, 1, figsize=(8, 12)) -> Option D

4. Quick Check:

   Rows=3, cols=1, figsize=(8,12) [OK]

Hint: Use figsize=(width, height) and rows, columns order [OK]

Common Mistakes:

• Swapping rows and columns
• Using wrong keyword 'size' instead of 'figsize'
• Confusing width and height order