Horizontal bar chart with plt.barh in Matplotlib - Mini Project: Build & Apply

Horizontal bar chart with plt.barh

📖 Scenario: You work in a small bakery and want to show how many cakes of each type you sold last week. You want to create a simple horizontal bar chart to share with your team.

🎯 Goal: Create a horizontal bar chart using plt.barh to display the number of cakes sold for each cake type.

📋 What You'll Learn

Create a list called cake_types with the cake names exactly as: 'Chocolate', 'Vanilla', 'Strawberry', 'Lemon', 'Carrot'

Create a list called cakes_sold with the numbers exactly as: 50, 40, 30, 20, 10

Use plt.barh to create a horizontal bar chart with cake_types on the y-axis and cakes_sold on the x-axis

Add labels for the x-axis as 'Number of Cakes Sold' and y-axis as 'Cake Type'

Display the chart using plt.show()

💡 Why This Matters

🌍 Real World

Horizontal bar charts are useful to compare categories when category names are long or when you want to display data horizontally for better readability.

💼 Career

Data analysts and scientists often use horizontal bar charts to present categorical data clearly in reports and presentations.

1

Create the data lists

Create a list called cake_types with these exact values: 'Chocolate', 'Vanilla', 'Strawberry', 'Lemon', 'Carrot'. Also create a list called cakes_sold with these exact numbers: 50, 40, 30, 20, 10.

Matplotlib

# Create the lists cake_types and cakes_sold with the exact values
# Your code here

Hint

Use square brackets [] to create lists. Separate items with commas.

2

Import matplotlib and set up the plot

Import matplotlib.pyplot as plt. This will allow you to create the chart.

Matplotlib

cake_types = ['Chocolate', 'Vanilla', 'Strawberry', 'Lemon', 'Carrot']
cakes_sold = [50, 40, 30, 20, 10]
# Import matplotlib.pyplot as plt
# Your code here

Hint

Use import matplotlib.pyplot as plt to import the plotting library.

3

Create the horizontal bar chart

Use plt.barh with cake_types as the y-values and cakes_sold as the x-values to create a horizontal bar chart. Then add x-axis label 'Number of Cakes Sold' and y-axis label 'Cake Type'.

Matplotlib

import matplotlib.pyplot as plt

cake_types = ['Chocolate', 'Vanilla', 'Strawberry', 'Lemon', 'Carrot']
cakes_sold = [50, 40, 30, 20, 10]
# Create horizontal bar chart with plt.barh
# Add x-axis label and y-axis label
# Your code here

Hint

Use plt.barh(y, x) where y is the list of categories and x is the list of values.

4

Display the chart

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

Matplotlib

import matplotlib.pyplot as plt

cake_types = ['Chocolate', 'Vanilla', 'Strawberry', 'Lemon', 'Carrot']
cakes_sold = [50, 40, 30, 20, 10]

plt.barh(cake_types, cakes_sold)
plt.xlabel('Number of Cakes Sold')
plt.ylabel('Cake Type')
# Display the plot
# Your code here

Hint

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

Practice

1. What does the plt.barh() function in matplotlib do?

easy

A. Generates a scatter plot with dots

B. Creates a vertical bar chart with bars extending bottom to top

C. Creates a horizontal bar chart with bars extending left to right

D. Plots a line graph connecting data points

Solution

1. Step 1: Understand the function purpose

   plt.barh() is designed to create horizontal bar charts, where bars extend from left to right.

2. Step 2: Compare with other plot types

   Vertical bar charts use plt.bar(), line graphs use plt.plot(), and scatter plots use plt.scatter().

3. Final Answer:

   Creates a horizontal bar chart with bars extending left to right -> Option C

4. Quick Check:

   Horizontal bar chart = plt.barh() [OK]

Hint: Remember 'h' in barh means horizontal bars [OK]

Common Mistakes:

• Confusing plt.barh() with plt.bar()
• Thinking plt.barh() creates vertical bars
• Mixing bar charts with line or scatter plots

2. Which of the following is the correct syntax to create a horizontal bar chart with categories ['A', 'B', 'C'] and values [5, 7, 3] using matplotlib?

easy

A. plt.barh(['A', 'B', 'C'], [5, 7, 3])

B. plt.bar([5, 7, 3], ['A', 'B', 'C'])

C. plt.barh([5, 7, 3], ['A', 'B', 'C'])

D. plt.plot(['A', 'B', 'C'], [5, 7, 3])

Solution

1. Step 1: Identify correct function and argument order

   plt.barh() takes categories as the first argument (y-axis labels) and values as the second argument (bar lengths).

2. Step 2: Check each option

   plt.barh(['A', 'B', 'C'], [5, 7, 3]) correctly uses plt.barh(['A', 'B', 'C'], [5, 7, 3]). plt.bar([5, 7, 3], ['A', 'B', 'C']) uses vertical bars and reverses arguments. plt.barh([5, 7, 3], ['A', 'B', 'C']) reverses arguments for horizontal bars. plt.plot(['A', 'B', 'C'], [5, 7, 3]) plots a line graph.

3. Final Answer:

   plt.barh(['A', 'B', 'C'], [5, 7, 3]) -> Option A

4. Quick Check:

   Categories first, values second in plt.barh() [OK]

Hint: In plt.barh(), categories come first, then values [OK]

Common Mistakes:

• Swapping categories and values in arguments
• Using plt.bar() instead of plt.barh() for horizontal bars
• Using plt.plot() instead of bar chart functions

3. What will be the output of the following code?

import matplotlib.pyplot as plt
categories = ['X', 'Y', 'Z']
values = [10, 5, 8]
plt.barh(categories, values, color='green')
plt.show()

medium

A. A vertical bar chart with green bars for categories X, Y, Z

B. A line plot connecting points (X,10), (Y,5), (Z,8)

C. An error because color must be a list

D. A horizontal bar chart with green bars for categories X, Y, Z

Solution

1. Step 1: Analyze the function and parameters

   The code uses plt.barh() with categories on y-axis and values as bar lengths, colored green.

2. Step 2: Understand the plot output

   This produces a horizontal bar chart with green bars labeled X, Y, Z with lengths 10, 5, and 8 respectively.

3. Final Answer:

   A horizontal bar chart with green bars for categories X, Y, Z -> Option D

4. Quick Check:

   plt.barh() + color='green' = horizontal green bars [OK]

Hint: plt.barh() always creates horizontal bars, color accepts string [OK]

Common Mistakes:

• Thinking plt.barh() creates vertical bars
• Assuming color must be a list
• Confusing bar chart with line plot

4. Identify the error in this code snippet that tries to create a horizontal bar chart:

import matplotlib.pyplot as plt
labels = ['A', 'B', 'C']
values = [4, 6, 8]
plt.barh(values, labels)
plt.show()

medium

A. plt.barh() does not accept lists as arguments

B. Arguments are reversed; categories should be first, values second

C. Missing plt.show() call

D. Color argument is required for plt.barh()

Solution

1. Step 1: Check argument order in plt.barh()

   The first argument should be categories (labels), the second argument should be values (bar lengths).

2. Step 2: Identify the mistake in the code

   The code passes values first and labels second, which reverses the expected order and causes incorrect plotting.

3. Final Answer:

   Arguments are reversed; categories should be first, values second -> Option B

4. Quick Check:

   plt.barh(categories, values) order matters [OK]

Hint: Categories first, values second in plt.barh() [OK]

Common Mistakes:

• Swapping the order of categories and values
• Forgetting plt.show() (though present here)
• Thinking color argument is mandatory

5. You have a dataset with categories ['Jan', 'Feb', 'Mar'] and sales [200, 150, 300]. You want to create a horizontal bar chart with red bars, bar height of 0.5, and display the sales values on the bars. Which code snippet correctly achieves this?

hard

A. plt.barh(['Jan', 'Feb', 'Mar'], [200, 150, 300], color='red', height=0.5)
for i, v in enumerate([200, 150, 300]):
plt.text(v + 5, i, str(v))
plt.show()

B. plt.barh([200, 150, 300], ['Jan', 'Feb', 'Mar'], color='red', height=0.5)
plt.show()

C. plt.bar(['Jan', 'Feb', 'Mar'], [200, 150, 300], color='red', height=0.5)
plt.show()

D. plt.barh(['Jan', 'Feb', 'Mar'], [200, 150, 300], color='red', width=0.5)
plt.show()

Solution

1. Step 1: Use plt.barh() with correct arguments

   Categories come first, then values. Set color='red' and height=0.5 to adjust bar thickness.

2. Step 2: Add sales values as text labels on bars

   Use a for loop with plt.text() to place sales numbers slightly right of each bar end.

3. Step 3: Verify other options

   plt.barh([200, 150, 300], ['Jan', 'Feb', 'Mar'], color='red', height=0.5) plt.show() reverses arguments, plt.bar(['Jan', 'Feb', 'Mar'], [200, 150, 300], color='red', height=0.5) plt.show() uses vertical bars, plt.barh(['Jan', 'Feb', 'Mar'], [200, 150, 300], color='red', width=0.5) plt.show() uses 'width' instead of 'height' which is invalid for barh.

4. Final Answer:

   plt.barh(['Jan', 'Feb', 'Mar'], [200, 150, 300], color='red', height=0.5) for i, v in enumerate([200, 150, 300]): plt.text(v + 5, i, str(v)) plt.show() -> Option A

5. Quick Check:

   plt.barh(categories, values, height=0.5) + plt.text() labels [OK]

Hint: Use height for bar thickness in plt.barh(), add labels with plt.text() [OK]

Common Mistakes:

• Swapping categories and values
• Using width instead of height for bar thickness
• Not adding text labels or placing them incorrectly