Horizontal bar chart with plt.barh in Matplotlib - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of plt.barh with given data

What will be the output of this code snippet that creates a horizontal bar chart?

Matplotlib

import matplotlib.pyplot as plt

categories = ['A', 'B', 'C']
values = [3, 7, 5]
plt.barh(categories, values)
plt.show()

A A vertical bar chart with bars for A=3, B=7, C=5

B SyntaxError due to wrong function usage

C A horizontal bar chart with bars for A=7, B=3, C=5

D A horizontal bar chart with bars for A=3, B=7, C=5

💡 Hint

plt.barh creates horizontal bars where the first argument is the y-axis labels and the second is the bar lengths.

plt.barh(categories, values) draws horizontal bars with categories on the y-axis and values as bar lengths. The order matches the lists.

❓ data_output

intermediate

Number of bars in plt.barh chart

How many bars will be displayed by this code?

Matplotlib

import matplotlib.pyplot as plt

labels = ['X', 'Y', 'Z', 'W']
values = [10, 20, 15, 5]
plt.barh(labels, values)
plt.show()

A 3

B 4

C 5

D 0

💡 Hint

Count the number of labels given to plt.barh.

There are 4 labels and 4 values, so 4 horizontal bars will be drawn.

🔧 Debug

advanced

Identify the error in horizontal bar chart code

What error will this code produce?

Matplotlib

import matplotlib.pyplot as plt

labels = ['Jan', 'Feb', 'Mar']
values = [5, 8]
plt.barh(labels, values)
plt.show()

A ValueError: y and width must be the same size

B TypeError: unsupported operand type(s)

C No error, chart displays correctly

D SyntaxError due to missing colon

💡 Hint

Check if the lengths of labels and values match.

plt.barh requires the labels and values lists to be the same length. Here, labels has 3 items but values has 2, causing a ValueError.

❓ visualization

advanced

Effect of changing bar height in plt.barh

What visual effect does changing the 'height' parameter in plt.barh have?

Matplotlib

import matplotlib.pyplot as plt

labels = ['P', 'Q', 'R']
values = [4, 6, 8]
plt.barh(labels, values, height=0.1)
plt.show()

A Bars change color

B Bars become wider horizontally

C Bars become thinner vertically

D Bars disappear

💡 Hint

Height controls the thickness of horizontal bars.

In plt.barh, the height parameter controls the thickness of each horizontal bar vertically. Smaller height means thinner bars.

🚀 Application

expert

Create a horizontal bar chart with sorted values

Which code snippet correctly creates a horizontal bar chart with categories sorted by their values in ascending order?

A

import matplotlib.pyplot as plt
categories = ['A', 'B', 'C']
values = [5, 2, 7]
sorted_pairs = sorted(zip(values, categories))
sorted_values, sorted_categories = zip(*sorted_pairs)
plt.barh(sorted_categories, sorted_values)
plt.show()

B

import matplotlib.pyplot as plt
categories = ['A', 'B', 'C']
values = [5, 2, 7]
plt.barh(categories.sort(), values.sort())
plt.show()

C

import matplotlib.pyplot as plt
categories = ['A', 'B', 'C']
values = [5, 2, 7]
plt.barh(sorted(categories), sorted(values))
plt.show()

D

import matplotlib.pyplot as plt
categories = ['A', 'B', 'C']
values = [5, 2, 7]
plt.barh(categories, values)
plt.show()

💡 Hint

You need to sort values and categories together to keep their pairs aligned.

Option A sorts the pairs of (value, category) so the bars appear in ascending order by value. Other options either misuse sort or break the pairing.

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