Bubble charts concept in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Bubble Chart Size Scaling

What will be the size of the bubbles in the plot generated by the following code snippet?

Matplotlib

import matplotlib.pyplot as plt
x = [1, 2, 3]
y = [4, 5, 6]
sizes = [10, 20, 30]
plt.scatter(x, y, s=sizes)
plt.show()
print(sizes)

A [100, 400, 900]

B [10, 20, 30]

C [1, 2, 3]

D [10, 20, 30, 40]

💡 Hint

The 's' parameter in plt.scatter controls the area of each bubble, not the radius.

The sizes list is passed directly to the 's' parameter, which sets the area of each bubble in points squared. The printed sizes list remains unchanged.

❓ data_output

intermediate

Number of Bubbles Displayed

Given the following data and code, how many bubbles will appear in the bubble chart?

Matplotlib

import matplotlib.pyplot as plt
x = [1, 2, 3, 4]
y = [10, 20, 30, 40]
sizes = [15, 25, 35]
plt.scatter(x, y, s=sizes)
plt.show()

A Raises ValueError

B 4

C 3

D 0

💡 Hint

The lengths of x, y, and sizes must match for plt.scatter.

The sizes list has fewer elements than x and y, causing a ValueError due to mismatched array lengths.

❓ visualization

advanced

Interpreting Bubble Chart Colors and Sizes

Consider this code that creates a bubble chart with color and size representing different data aspects. What does the color represent in the resulting plot?

Matplotlib

import matplotlib.pyplot as plt
import numpy as np
x = np.array([5, 15, 25, 35, 45])
y = np.array([10, 20, 30, 40, 50])
sizes = np.array([100, 200, 300, 400, 500])
colors = np.array([1, 2, 3, 4, 5])
plt.scatter(x, y, s=sizes, c=colors, cmap='viridis')
plt.colorbar()
plt.show()

A The colors represent the sizes of the bubbles.

B The colors represent the x-axis values.

C The colors are randomly assigned and do not represent any data.

D The colors represent the values in the 'colors' array, mapped to the 'viridis' color scale.

💡 Hint

The 'c' parameter controls color mapping in plt.scatter.

The 'c' parameter is set to the 'colors' array, so bubble colors correspond to these values mapped through the 'viridis' colormap.

🔧 Debug

advanced

Identify the Error in Bubble Chart Code

What error will this code produce when run?

Matplotlib

import matplotlib.pyplot as plt
x = [1, 2, 3]
y = [4, 5]
sizes = [10, 20, 30]
plt.scatter(x, y, s=sizes)
plt.show()

A ValueError: x and y must be the same size

B TypeError: sizes must be a scalar or array-like

C IndexError: list index out of range

D No error, plot displays correctly

💡 Hint

Check if x and y have the same number of elements.

x has 3 elements but y has 2, causing ValueError due to mismatched input sizes for scatter plot.

🚀 Application

expert

Choosing Bubble Sizes for Visual Clarity

You have data points with values ranging from 1 to 1000. You want to create a bubble chart where bubble sizes reflect these values but remain visually clear and not too large. Which approach is best to set the bubble sizes?

A Use the raw values directly as sizes in plt.scatter.

B Use the logarithm (base 10) of the values as sizes without scaling.

C Apply a square root transformation to the values before passing as sizes.

D Normalize values between 0 and 1 and use them directly as sizes.

💡 Hint

Bubble area grows with the size parameter, so large raw values can cause huge bubbles.

Applying square root to values before sizing keeps bubble areas proportional to data but prevents very large bubbles, improving visual clarity.

Practice

1. What does the size of bubbles represent in a bubble chart created with matplotlib?

easy

A. The color of the bubbles

B. A third data value representing magnitude or quantity

C. The x-axis position

D. The y-axis position

Solution

1. Step 1: Understand bubble chart data dimensions

   A bubble chart shows data points with x and y coordinates plus a size dimension.

2. Step 2: Identify what bubble size represents

   The size of each bubble encodes a third data value, like quantity or magnitude.

3. Final Answer:

   A third data value representing magnitude or quantity -> Option B

4. Quick Check:

   Bubble size = third data value [OK]

Hint: Bubble size shows extra data beyond x and y [OK]

Common Mistakes:

• Confusing size with color
• Thinking size is x or y position
• Ignoring the third data dimension

2. Which matplotlib function parameter controls the bubble sizes in a bubble chart?

easy

A. size

B. bubble_size

C. radius

D. s

Solution

1. Step 1: Recall plt.scatter parameters

   The plt.scatter function uses s to set bubble sizes.

2. Step 2: Confirm correct parameter name

   Other options like size or radius are not valid parameters for bubble size in plt.scatter.

3. Final Answer:

   s -> Option D

4. Quick Check:

   plt.scatter(x, y, s=...) sets bubble size [OK]

Hint: Use 's' parameter for bubble sizes in plt.scatter [OK]

Common Mistakes:

• Using 'size' instead of 's'
• Trying 'radius' which is invalid
• Confusing with color parameter

3. What will be the output of this code snippet?

import matplotlib.pyplot as plt
x = [1, 2, 3]
y = [4, 5, 6]
sizes = [100, 200, 300]
plt.scatter(x, y, s=sizes)
plt.show()

medium

A. A syntax error due to incorrect parameter

B. A scatter plot with all bubbles the same size

C. A scatter plot with three bubbles sized 100, 200, and 300 respectively

D. A scatter plot with bubbles sized 1, 2, and 3

Solution

1. Step 1: Analyze the code parameters

   The code uses plt.scatter with x, y coordinates and s=sizes where sizes are [100, 200, 300].

2. Step 2: Understand bubble size mapping

   Each bubble size corresponds to the values in the sizes list, so bubbles will have sizes 100, 200, and 300.

3. Final Answer:

   A scatter plot with three bubbles sized 100, 200, and 300 respectively -> Option C

4. Quick Check:

   Bubble sizes match 's' list values [OK]

Hint: Bubble sizes come from the 's' list values [OK]

Common Mistakes:

• Assuming all bubbles have same size
• Confusing sizes with x or y values
• Expecting syntax error incorrectly

4. Identify the error in this bubble chart code:

import matplotlib.pyplot as plt
x = [1, 2, 3]
y = [4, 5, 6]
sizes = [100, 200]
plt.scatter(x, y, s=sizes)
plt.show()

medium

A. The sizes list length does not match x and y lengths

B. The parameter 's' is misspelled

C. x and y must be strings, not lists

D. plt.scatter cannot plot more than two points

Solution

1. Step 1: Check lengths of x, y, and sizes

   x and y have 3 elements each, but sizes has only 2 elements.

2. Step 2: Understand size array length requirement

   The sizes array must match the number of points to assign size to each bubble.

3. Final Answer:

   The sizes list length does not match x and y lengths -> Option A

4. Quick Check:

   Sizes length must equal x and y length [OK]

Hint: Sizes array length must match x and y arrays [OK]

Common Mistakes:

• Ignoring size list length mismatch
• Thinking 's' parameter is misspelled
• Believing x and y must be strings

5. You want to create a bubble chart where bubble sizes represent sales volume, but sales data has zeros and very large values. Which approach is best to make the chart readable?

hard

A. Normalize sales data and apply a size scaling factor

B. Use raw sales values directly as sizes

C. Set all bubble sizes to a fixed constant

D. Use sales data as x-axis values instead

Solution

1. Step 1: Understand impact of raw sizes

   Using raw sales values with zeros and large numbers causes bubbles too small or too large, making chart unreadable.

2. Step 2: Normalize and scale sizes

   Normalizing sales data (e.g., min-max scaling) and applying a size factor keeps bubbles proportional and visible.

3. Step 3: Evaluate other options

   Fixed sizes lose data meaning; using sales as x-axis changes chart type and loses size info.

4. Final Answer:

   Normalize sales data and apply a size scaling factor -> Option A

5. Quick Check:

   Normalize and scale sizes for readability [OK]

Hint: Normalize and scale sizes to handle zeros and extremes [OK]

Common Mistakes:

• Using raw sizes causing unreadable bubbles
• Fixing all sizes losing data info
• Misusing sales data as axis instead of size