Bar plots in Pandas - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple bar plot code

What will be the output of the following code snippet that creates a bar plot using pandas?

Pandas

import pandas as pd
import matplotlib.pyplot as plt

data = {'fruits': ['apple', 'banana', 'cherry'], 'counts': [10, 15, 7]}
df = pd.DataFrame(data)
df.plot.bar(x='fruits', y='counts')
plt.close()  # Prevent plot display in some environments
print(df['counts'].sum())

A 15

B 32

C 10

D 3

💡 Hint

Think about what the sum of the 'counts' column is.

The code creates a DataFrame with counts 10, 15, and 7. The sum of these counts is 32, which is printed as output.

❓ data_output

intermediate

Number of bars in grouped bar plot

Given the following DataFrame and code, how many bars will the resulting grouped bar plot display?

Pandas

import pandas as pd
import matplotlib.pyplot as plt

data = {'year': [2020, 2020, 2021, 2021], 'category': ['A', 'B', 'A', 'B'], 'value': [5, 7, 6, 8]}
df = pd.DataFrame(data)
df_pivot = df.pivot(index='year', columns='category', values='value')
df_pivot.plot.bar()
plt.close()

A 1

B 2

C 4

D 3

💡 Hint

Count the number of bars per group and the number of groups.

There are 2 years (groups) and 2 categories (bars per group), so total bars = 2 * 2 = 4.

🔧 Debug

advanced

Identify the error in bar plot code

What error will this code raise when trying to create a bar plot?

Pandas

import pandas as pd
import matplotlib.pyplot as plt

data = {'items': ['pen', 'pencil', 'eraser'], 'counts': ['10', '15', '7']}
df = pd.DataFrame(data)
df.plot.bar(x='items', y='counts')
plt.close()

A No error, plot displays correctly

B TypeError: unsupported operand type(s) for +: 'int' and 'str'

C ValueError: could not convert string to float: 'pen'

D TypeError: unhashable type: 'list'

💡 Hint

Check the data types of the 'counts' column.

The 'counts' column contains strings, but pandas and matplotlib can handle numeric strings for plotting without error.

❓ visualization

advanced

Bar plot with stacked bars

What will the stacked bar plot display when running this code?

Pandas

import pandas as pd
import matplotlib.pyplot as plt

data = {'Q1': [3, 5], 'Q2': [4, 6]}
index = ['Product A', 'Product B']
df = pd.DataFrame(data, index=index)
df.plot.bar(stacked=True)
plt.close()

A A line plot connecting Q1 and Q2 values

B A pie chart showing total sums of Q1 and Q2

C Four separate bars, two for Q1 and two for Q2

D Two bars, each divided into two stacked segments representing Q1 and Q2 values

💡 Hint

Stacked bars combine segments vertically in one bar per index.

The plot shows one bar per product with Q1 and Q2 values stacked on top of each other.

🧠 Conceptual

expert

Effect of setting figsize in bar plots

How does changing the figsize parameter affect a pandas bar plot?

A It changes the size of the entire plot area, making bars and labels larger or smaller accordingly

B It changes only the width of the bars but not the height of the plot

C It changes the color of the bars automatically based on size

D It changes the data values plotted on the bars

💡 Hint

Think about what 'figsize' means in matplotlib plots.

The figsize parameter controls the overall size of the figure, affecting how big the bars and labels appear.