Horizontal grouped bars in Matplotlib - Mini Project: Build & Apply

Horizontal grouped bars

📖 Scenario: You are working for a small company that wants to compare sales of two products across three regions. They want a clear visual to see which product sells better in each region.

🎯 Goal: Create a horizontal grouped bar chart using matplotlib to compare sales of two products across three regions.

📋 What You'll Learn

Create a list called regions with the values 'North', 'South', and 'East'.

Create two lists called sales_product_a and sales_product_b with sales numbers for each region.

Create a variable called bar_width and set it to 0.4.

Use matplotlib.pyplot to create horizontal grouped bars for both products side by side for each region.

Add labels for the y-axis with region names and a legend for the products.

Display the plot.

💡 Why This Matters

🌍 Real World

Horizontal grouped bar charts are useful to compare multiple categories side by side across different groups, such as sales of different products in various regions.

💼 Career

Data analysts and scientists often create grouped bar charts to visualize and communicate comparisons clearly to stakeholders.

1

Create the sales data lists

Create a list called regions with the values 'North', 'South', and 'East'. Then create two lists called sales_product_a with values 120, 150, 100 and sales_product_b with values 90, 130, 110.

Matplotlib

# Create the regions and sales lists
# Your code here

Hint

Use square brackets to create lists. Put the region names as strings in regions. Put the sales numbers as integers in sales_product_a and sales_product_b.

2

Set the bar width

Create a variable called bar_width and set it to 0.4.

Matplotlib

regions = ['North', 'South', 'East']
sales_product_a = [120, 150, 100]
sales_product_b = [90, 130, 110]
# Create bar_width variable
# Your code here

Hint

Just assign the number 0.4 to the variable bar_width.

3

Create the horizontal grouped bars

Import matplotlib.pyplot as plt. Create a list called y_positions using range(len(regions)). Use plt.barh() to plot sales_product_a at y_positions with height bar_width. Then plot sales_product_b at [y + bar_width for y in y_positions] with height bar_width. Add y-axis ticks at the middle of the grouped bars with region names using plt.yticks(). Add a legend with labels 'Product A' and 'Product B'.

Matplotlib

import matplotlib.pyplot as plt

regions = ['North', 'South', 'East']
sales_product_a = [120, 150, 100]
sales_product_b = [90, 130, 110]
bar_width = 0.4

# Create y_positions list
# Plot horizontal bars for Product A and Product B
# Set y-axis ticks and legend
# Your code here

Hint

Use plt.barh() twice with adjusted y positions to create grouped bars. Use plt.yticks() to label the regions in the middle of the groups.

4

Display the plot

Use plt.show() to display the horizontal grouped bar chart.

Matplotlib

import matplotlib.pyplot as plt

regions = ['North', 'South', 'East']
sales_product_a = [120, 150, 100]
sales_product_b = [90, 130, 110]
bar_width = 0.4

y_positions = list(range(len(regions)))

plt.barh(y_positions, sales_product_a, height=bar_width, label='Product A')
plt.barh([y + bar_width for y in y_positions], sales_product_b, height=bar_width, label='Product B')

plt.yticks([y + bar_width / 2 for y in y_positions], regions)
plt.legend()

# Display the plot
# Your code here

Hint

Call plt.show() to display the chart window.

Practice

1.

What is the main purpose of using horizontal grouped bars in a chart?

easy

A. To compare multiple categories side by side horizontally

B. To show data as a pie chart

C. To display data only vertically

D. To create a line graph

Solution

1. Step 1: Understand the chart type

   Horizontal grouped bars place bars side by side horizontally to compare groups.

2. Step 2: Identify the purpose

   This layout helps compare multiple categories clearly across groups.

3. Final Answer:

   To compare multiple categories side by side horizontally -> Option A

4. Quick Check:

   Horizontal grouped bars = compare categories horizontally [OK]

Hint: Grouped bars show side-by-side comparisons horizontally [OK]

Common Mistakes:

• Confusing horizontal bars with pie charts
• Thinking grouped bars are vertical only
• Mixing line graphs with bar charts

2.

Which of the following is the correct way to create horizontal grouped bars in matplotlib?

import matplotlib.pyplot as plt
import numpy as np

labels = ['A', 'B', 'C']
values1 = [5, 7, 3]
values2 = [6, 2, 4]

x = np.arange(len(labels))
width = 0.35

plt.barh(x, values1, height=width)
plt.barh(x + width, values2, height=width)
plt.show()

easy

A. Use plt.scatter for grouped bars

B. Use plt.bar with shifted positions for each group

C. Use plt.plot with x and y values

D. Use plt.barh with shifted positions for each group

Solution

1. Step 1: Check the function used

   The code uses plt.barh which creates horizontal bars.

2. Step 2: Verify grouping method

   Positions are shifted by adding width to x to group bars side by side horizontally.

3. Final Answer:

   Use plt.barh with shifted positions for each group -> Option D

4. Quick Check:

   plt.barh + shifted positions = grouped horizontal bars [OK]

Hint: Use plt.barh and shift positions to group bars horizontally [OK]

Common Mistakes:

• Using plt.bar instead of plt.barh for horizontal bars
• Not shifting positions causing overlapping bars
• Using plt.plot or plt.scatter which are not bar charts

3.

What will be the output of the following code?

import matplotlib.pyplot as plt
import numpy as np

labels = ['X', 'Y']
values1 = [3, 8]
values2 = [5, 2]

x = np.arange(len(labels))
width = 0.4

plt.barh(x, values1, height=width, color='blue')
plt.barh(x + width, values2, height=width, color='red')
plt.yticks(x + width / 2, labels)
plt.show()

medium

A. A line plot with two lines

B. Two vertical bar groups overlapping

C. Two sets of horizontal bars side by side for each label

D. A scatter plot with points at x positions

Solution

1. Step 1: Analyze barh usage

   plt.barh creates horizontal bars at positions x and x + width, shifted to group bars.

2. Step 2: Check y-axis labels

   yticks are set at middle positions between bars for labels 'X' and 'Y'.

3. Final Answer:

   Two sets of horizontal bars side by side for each label -> Option C

4. Quick Check:

   barh + shifted positions + ytick labels = grouped horizontal bars [OK]

Hint: Shift y positions and set yticks for grouped horizontal bars [OK]

Common Mistakes:

• Confusing horizontal bars with vertical bars
• Not setting yticks causing label misalignment
• Expecting line or scatter plot output

4.

Identify the error in this code for horizontal grouped bars:

import matplotlib.pyplot as plt
import numpy as np

labels = ['P', 'Q', 'R']
values1 = [4, 6, 5]
values2 = [7, 3, 8]

x = np.arange(len(labels))
width = 0.3

plt.barh(x, values1, height=width)
plt.barh(x, values2, height=width)
plt.yticks(x + width / 2, labels)
plt.show()

medium

A. Bars overlap because positions are not shifted for grouping

B. Height parameter is missing

C. yticks are set incorrectly

D. Values lists have different lengths

Solution

1. Step 1: Check bar positions

   Both plt.barh calls use the same x positions, so bars overlap instead of grouping.

2. Step 2: Verify grouping method

   Positions should be shifted by width to separate groups horizontally.

3. Final Answer:

   Bars overlap because positions are not shifted for grouping -> Option A

4. Quick Check:

   Same x positions without shift = overlapping bars [OK]

Hint: Shift bar positions to avoid overlap in grouped bars [OK]

Common Mistakes:

• Not shifting positions for second group
• Incorrect yticks placement
• Assuming height parameter fixes overlap

5.

You have sales data for 3 products over 2 years:

products = ['A', 'B', 'C']
year1 = [10, 15, 7]
year2 = [12, 9, 14]

How would you create a horizontal grouped bar chart to compare sales by product and year, ensuring product labels appear centered between grouped bars?

hard

A. Use plt.plot to draw lines for each product

B. Use plt.barh with positions shifted by width and set yticks at x + width/2

C. Use plt.barh with same positions for both years and set yticks at x

D. Use plt.bar with positions shifted by width and set xticks at x + width/2

Solution

1. Step 1: Use plt.barh with shifted positions

   Shift positions by width for each year to group bars horizontally side by side.

2. Step 2: Set yticks at middle of grouped bars

   Set yticks at x + width/2 so product labels appear centered between bars.

3. Final Answer:

   Use plt.barh with positions shifted by width and set yticks at x + width/2 -> Option B

4. Quick Check:

   Shift positions + yticks center = clear grouped horizontal bars [OK]

Hint: Shift bars and center yticks for clear grouped horizontal bars [OK]

Common Mistakes:

• Using vertical bars instead of horizontal
• Not shifting positions causing overlap
• Setting yticks incorrectly causing label misalignment