MultiIndex (hierarchical indexing) in Data Analysis Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this MultiIndex selection?

Given the DataFrame with a MultiIndex, what will be the output of selecting data.loc['B']?

Data Analysis Python

import pandas as pd

index = pd.MultiIndex.from_tuples([('A', 1), ('A', 2), ('B', 1), ('B', 2)])
data = pd.DataFrame({'Value': [10, 20, 30, 40]}, index=index)
result = data.loc['B']
print(result)

A

   Value
1     30
2     40

B

Value
1    30
2    40

C

Value
B    30
B    40

D KeyError: 'B'

💡 Hint

Remember that selecting with a level value returns a DataFrame or Series indexed by the remaining level(s).

When selecting data.loc['B'], pandas returns all rows where the first level of the MultiIndex is 'B'. The resulting DataFrame is indexed by the second level (1 and 2) with the 'Value' column.

❓ data_output

intermediate

How many rows are in the DataFrame after slicing with .loc?

Given the MultiIndex DataFrame below, how many rows remain after slicing with data.loc[('A', slice(1,2))]?

Data Analysis Python

import pandas as pd

index = pd.MultiIndex.from_tuples([('A', 1), ('A', 2), ('A', 3), ('B', 1)])
data = pd.DataFrame({'Value': [10, 20, 30, 40]}, index=index)
sliced = data.loc[('A', slice(1,2))]
print(len(sliced))

A 1

B 2

C 3

D 4

💡 Hint

Slice selects rows where the second level is between 1 and 2 inclusive.

The slice selects rows with first level 'A' and second level 1 or 2. There are exactly two such rows.

❓ visualization

advanced

Which plot shows the correct aggregation by first level of MultiIndex?

Given a MultiIndex DataFrame with sales data, which plot correctly shows the total sales summed by the first level of the index?

Data Analysis Python

import pandas as pd
import matplotlib.pyplot as plt

index = pd.MultiIndex.from_tuples([('Store1', 'Jan'), ('Store1', 'Feb'), ('Store2', 'Jan'), ('Store2', 'Feb')])
data = pd.DataFrame({'Sales': [100, 150, 200, 250]}, index=index)

agg = data.groupby(level=0).sum()
agg.plot(kind='bar')
plt.show()

A Scatter plot with points for each sale value

B Line plot with four points labeled Store1-Jan, Store1-Feb, Store2-Jan, Store2-Feb

C Pie chart with four slices for each month

D Bar plot with two bars labeled Store1 and Store2 showing heights 250 and 450

💡 Hint

Grouping by level=0 sums sales per store.

The groupby(level=0).sum() aggregates sales by the first index level (store). The bar plot shows total sales per store.

🔧 Debug

advanced

What error does this MultiIndex slicing code raise?

What error will this code raise when trying to slice a MultiIndex DataFrame?

Data Analysis Python

import pandas as pd

index = pd.MultiIndex.from_tuples([('X', 1), ('X', 2), ('Y', 1)])
data = pd.DataFrame({'Value': [5, 10, 15]}, index=index)

result = data.loc['X', 1:2]
print(result)

A IndexingError: Too many indexers

B KeyError: 1

C TypeError: unhashable type: 'slice'

D No error, prints the sliced DataFrame

💡 Hint

Check how .loc handles multiple indexers with MultiIndex.

Using data.loc['X', 1:2] tries to index with two separate arguments, but .loc expects a tuple for MultiIndex slicing. This causes an IndexingError.

🚀 Application

expert

What is the resulting DataFrame after swapping levels and sorting?

Given a MultiIndex DataFrame, what is the output after swapping the index levels and sorting by the new index?

Data Analysis Python

import pandas as pd

index = pd.MultiIndex.from_tuples([('C', 2), ('A', 1), ('B', 3)])
data = pd.DataFrame({'Score': [30, 10, 20]}, index=index)

swapped = data.swaplevel(0, 1).sort_index()
print(swapped)

A

       Score
A 1    10
B 3    20
C 2    30

B

       Score
1     10
2     30
3     20

C

       Score
1 A     10
2 C     30
3 B     20

D KeyError: 0

💡 Hint

Swapping levels changes the order of index levels, then sorting arranges by the new first level.

swaplevel(0,1) switches the two index levels. Sorting by index then orders by the new first level (previously second level). The output shows index with first level 1,2,3 and second level A,C,B respectively.