Bar charts in Data Analysis Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple bar chart code

What will be the output of this Python code using matplotlib?

Data Analysis Python

import matplotlib.pyplot as plt

categories = ['A', 'B', 'C']
values = [5, 3, 9]
plt.bar(categories, values)
plt.show()

A A bar chart with three bars labeled A, B, C with heights 5, 3, and 9 respectively

B A line chart connecting points (A,5), (B,3), (C,9)

C A scatter plot with points at (A,5), (B,3), (C,9)

D A pie chart showing proportions of 5, 3, and 9

💡 Hint

Look at the function plt.bar and what it does with categories and values.

plt.bar creates vertical bars for each category with heights from values. plt.show() displays the chart.

❓ data_output

intermediate

Data output from grouped bar chart data

Given this data for two groups, what is the total height of bars for category 'X'?

Data Analysis Python

import pandas as pd

data = {'Category': ['X', 'Y', 'Z'], 'Group1': [4, 7, 1], 'Group2': [3, 2, 5]}
df = pd.DataFrame(data)
total_x = df.loc[df['Category'] == 'X', ['Group1', 'Group2']].sum(axis=1).values[0]
print(total_x)

A 3

B 4

C 12

D 7

💡 Hint

Sum the values for Group1 and Group2 where Category is 'X'.

For category 'X', Group1 has 4 and Group2 has 3. Their sum is 7.

❓ visualization

advanced

Identify the error in this stacked bar chart code

What error will this code produce when trying to plot a stacked bar chart?

Data Analysis Python

import matplotlib.pyplot as plt

labels = ['G1', 'G2', 'G3']
men_means = [20, 35, 30]
women_means = [25, 32, 34]

plt.bar(labels, men_means)
plt.bar(labels, women_means, bottom=men_means)
plt.show()

A No error; the code produces a stacked bar chart correctly

B TypeError because bottom parameter expects a scalar, not a list

C ValueError due to mismatched lengths of labels and data

D RuntimeWarning about overlapping bars

💡 Hint

Check how plt.bar handles the bottom parameter with lists.

plt.bar accepts a list for bottom to stack bars. The code runs without error and produces a stacked bar chart.

🔧 Debug

advanced

Why does this horizontal bar chart code fail?

This code is intended to create a horizontal bar chart but raises an error. What is the cause?

Data Analysis Python

import matplotlib.pyplot as plt

categories = ['A', 'B', 'C']
values = [10, 20, 15]
plt.barh(categories, values, color='blue')
plt.xlabel('Categories')
plt.ylabel('Values')
plt.show()

A TypeError because plt.barh does not accept color argument

B No error; the code runs and shows a horizontal bar chart

C ValueError because xlabel and ylabel are swapped

D AttributeError because plt.barh is not a valid function

💡 Hint

Check if plt.barh exists and accepts color argument.

plt.barh is a valid function and accepts color. xlabel and ylabel can be set in any order. The code runs fine.

🚀 Application

expert

Calculate the number of bars in a grouped bar chart

You have a DataFrame with 4 categories and 3 groups. You want to plot a grouped bar chart showing all groups side by side for each category. How many bars will appear in total?

Data Analysis Python

import pandas as pd

data = {'Category': ['C1', 'C2', 'C3', 'C4'], 'Group1': [5, 7, 6, 8], 'Group2': [3, 2, 4, 1], 'Group3': [9, 5, 7, 6]}
df = pd.DataFrame(data)

A 7

B 3

C 12

D 4

💡 Hint

Multiply the number of categories by the number of groups.

Each category has 3 groups, so total bars = 4 categories * 3 groups = 12 bars.