isin() for value matching in Pandas - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of isin() with multiple values

What is the output of this code snippet?

Pandas

import pandas as pd

s = pd.Series([10, 20, 30, 40, 50])
result = s.isin([20, 40, 60])
print(result.tolist())

A [True, False, True, False, True]

B [True, True, False, True, False]

C [False, False, False, False, False]

D [False, True, False, True, False]

💡 Hint

Check which values in the series are exactly in the list [20, 40, 60].

The isin() method returns True for elements that are in the given list. Here, 20 and 40 are in the list, so their positions are True; others are False.

❓ data_output

intermediate

Filtering DataFrame rows using isin()

Given the DataFrame below, which rows remain after filtering with isin()?

Pandas

import pandas as pd

df = pd.DataFrame({
    'Name': ['Anna', 'Bob', 'Cathy', 'David'],
    'City': ['NY', 'LA', 'NY', 'Chicago']
})
filtered = df[df['City'].isin(['NY', 'Chicago'])]
print(filtered)

A

   Name     City
0  Anna       NY
2  Cathy      NY
3  David  Chicago

B

   Name     City
1  Bob        LA
3  David  Chicago

C

   Name     City
0  Anna       NY
1  Bob        LA

D

   Name     City
2  Cathy      NY
3  David  Chicago

💡 Hint

Look for rows where City is either 'NY' or 'Chicago'.

Rows with City 'NY' or 'Chicago' are kept. That includes Anna, Cathy, and David.

🧠 Conceptual

advanced

Behavior of isin() with empty list

What is the output of this code snippet?

Pandas

import pandas as pd

s = pd.Series([1, 2, 3])
result = s.isin([])
print(result.tolist())

A [True, True, True]

B [False, False, False]

C []

D [None, None, None]

💡 Hint

Think about what it means to check if values are in an empty list.

No values can be in an empty list, so all results are False.

🔧 Debug

advanced

Error caused by wrong argument type in isin()

What error does this code raise?

Pandas

import pandas as pd

s = pd.Series([1, 2, 3])
result = s.isin(2)
print(result)

A TypeError: argument of type 'int' is not iterable

B ValueError: wrong number of arguments

C AttributeError: 'int' object has no attribute 'isin'

D No error, outputs [False, True, False]

💡 Hint

Check what type the argument to isin() should be.

isin() expects an iterable like list or set. Passing an int causes a TypeError because int is not iterable.

🚀 Application

expert

Count how many DataFrame rows match multiple conditions using isin()

Given this DataFrame, how many rows have 'Category' in ['A', 'C'] and 'Score' in [10, 30]?

Pandas

import pandas as pd

df = pd.DataFrame({
    'Category': ['A', 'B', 'C', 'A', 'B', 'C'],
    'Score': [10, 20, 30, 40, 10, 30]
})
filtered = df[df['Category'].isin(['A', 'C']) & df['Score'].isin([10, 30])]
count = filtered.shape[0]
print(count)

A 5

B 4

C 3

D 2

💡 Hint

Check rows where Category is 'A' or 'C' and Score is 10 or 30 simultaneously.

Rows matching both conditions are: (A,10), (C,30), and (C,30) again. Total 3 rows.