Marker size variation in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of varying marker sizes in scatter plot

What will be the output of the following code snippet that uses matplotlib to plot points with different marker sizes?

Matplotlib

import matplotlib.pyplot as plt
sizes = [20, 50, 80, 200]
x = [1, 2, 3, 4]
y = [10, 20, 25, 30]
plt.scatter(x, y, s=sizes)
plt.show()

A A scatter plot with 4 points, each point having marker sizes 20, 50, 80, and 200 respectively.

B A scatter plot with 4 points, but all markers are invisible because size is zero.

C A scatter plot with 4 points, all having the same marker size equal to the sum of sizes list.

D A scatter plot with 4 points, but marker sizes are ignored and default size is used.

💡 Hint

The 's' parameter in plt.scatter controls the marker size for each point individually if given a list.

The 's' argument accepts a list of sizes, so each point gets its own size. The plot will show points with sizes 20, 50, 80, and 200 respectively.

❓ data_output

intermediate

Number of points with marker size greater than 50

Given the following code, how many points have marker sizes greater than 50?

Matplotlib

import matplotlib.pyplot as plt
sizes = [10, 60, 45, 90, 30]
x = [1, 2, 3, 4, 5]
y = [5, 15, 10, 20, 25]
plt.scatter(x, y, s=sizes)
plt.show()

A 3

B 2

C 1

D 4

💡 Hint

Check the sizes list and count how many values are greater than 50.

Only the sizes 60 and 90 are greater than 50, so 2 points have marker sizes greater than 50.

🔧 Debug

advanced

Identify the error in marker size assignment

What error will this code raise when trying to plot marker sizes?

Matplotlib

import matplotlib.pyplot as plt
sizes = '20, 40, 60'
x = [1, 2, 3]
y = [5, 10, 15]
plt.scatter(x, y, s=sizes)
plt.show()

A TypeError: float() argument must be a string or a number, not 'tuple'

B No error, plot displays with marker sizes 20, 40, 60

C TypeError: 'str' object is not iterable

D ValueError: s must be a scalar or sequence of scalars

💡 Hint

Check the type of 'sizes' and what plt.scatter expects for 's'.

The 'sizes' variable is a string, not a list or array of numbers. plt.scatter expects a scalar or sequence of numbers for 's'. Passing a string causes a ValueError.

❓ visualization

advanced

Effect of marker size scaling on scatter plot

Which option correctly describes the visual difference when doubling the marker sizes in this scatter plot?

Matplotlib

import matplotlib.pyplot as plt
sizes = [30, 60, 90]
x = [1, 2, 3]
y = [10, 20, 30]
plt.scatter(x, y, s=[size * 2 for size in sizes])
plt.show()

A Markers appear the same size as original because scaling is ignored.

B Markers appear twice as large in diameter compared to original sizes.

C Markers appear twice as large in area compared to original sizes.

D Markers appear half the size of original because sizes are divided.

💡 Hint

Remember that 's' controls marker area, not diameter.

The 's' parameter controls the area of markers. Doubling 's' doubles the area, so markers appear larger but diameter increases by sqrt(2), not 2.

🚀 Application

expert

Create a scatter plot with marker sizes proportional to y-values

Which code snippet correctly creates a scatter plot where marker sizes are proportional to the y-values multiplied by 10?

A plt.scatter(x, y, s=[val * 10 for val in y])

B plt.scatter(x, y, s=y * 10)

C plt.scatter(x, y, s=[y * 10])

D plt.scatter(x, y, s=list(map(lambda x: x*10, x)))

💡 Hint

You need to multiply each y-value by 10 to get marker sizes.

Option A correctly multiplies each y-value by 10 using a list comprehension. Option A causes a TypeError because y is a list and cannot be multiplied directly. Option A creates a list with one element, not sizes for each point. Option A multiplies x-values, not y-values.