Bar width and positioning in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Bar chart with custom bar width

What is the width of each bar in the resulting bar chart from this code?

Matplotlib

import matplotlib.pyplot as plt

x = [1, 2, 3]
heights = [4, 5, 6]
plt.bar(x, heights, width=0.5)
plt.show()

A 0.8

B 0.3

C 1.0

D 0.5

💡 Hint

Look at the width parameter in plt.bar function.

The width parameter controls the width of each bar. Here it is set to 0.5, so each bar is half a unit wide.

❓ data_output

intermediate

Positions of grouped bars

Given two groups of bars plotted side by side with width 0.4, what are the x positions of the bars in the second group?

Matplotlib

import numpy as np
import matplotlib.pyplot as plt

labels = ['A', 'B', 'C']
x = np.arange(len(labels))
width = 0.4

plt.bar(x - width/2, [1, 2, 3], width=width)
plt.bar(x + width/2, [4, 5, 6], width=width)
plt.show()

positions_second_group = x + width/2
print(positions_second_group)

A [0.2 1.2 2.2]

B [-0.2 0.8 1.8]

C [0.4 1.4 2.4]

D [0.0 1.0 2.0]

💡 Hint

Positions are shifted by half the bar width to the right for the second group.

The second group bars are positioned at x + width/2, which shifts them 0.2 units right if width=0.4.

❓ visualization

advanced

Effect of bar width on bar overlap

Which bar width will cause the bars to overlap when plotted at positions [0, 1, 2]?

Matplotlib

import matplotlib.pyplot as plt

x = [0, 1, 2]
heights = [3, 4, 5]

plt.bar(x, heights, width=1.2)
plt.show()

A 0.5

B 0.8

C 1.2

D 1.0

💡 Hint

Bars overlap if width is greater than the distance between bar centers.

Bars are centered at positions 0,1,2. Distance between centers is 1. Width 1.2 is greater than 1, so bars overlap.

🧠 Conceptual

advanced

Understanding bar alignment parameter

What does setting the 'align' parameter to 'edge' do in plt.bar compared to the default 'center'?

A Bars are aligned so their left edges are at the x positions instead of centers.

B Bars are aligned so their centers are at the x positions (default behavior).

C Bars are aligned so their right edges are at the x positions.

D Bars are stacked vertically instead of side by side.

💡 Hint

Think about where the bar starts relative to the x coordinate.

With align='edge', the x positions mark the left edge of each bar, not the center.

🔧 Debug

expert

Fixing incorrect bar positions in grouped bar chart

Given this code, which option correctly fixes the bar positions so the two groups do not overlap?

Matplotlib

import numpy as np
import matplotlib.pyplot as plt

labels = ['X', 'Y', 'Z']
x = np.arange(len(labels))
width = 0.3

plt.bar(x, [5, 7, 9], width=width)
plt.bar(x, [6, 8, 10], width=width)
plt.show()

A Change second plt.bar to plt.bar(x + width, [6, 8, 10], width=width)

B Change first plt.bar to plt.bar(x - width/2, [5, 7, 9], width=width) and second to plt.bar(x + width/2, [6, 8, 10], width=width)

C Change second plt.bar to plt.bar(x - width, [6, 8, 10], width=width)

D Change width to 0.6 for both bars

💡 Hint

To avoid overlap, shift bars left and right by half the width.

Option B correctly shifts the two groups left and right by half the bar width, so they sit side by side without overlap.