String methods on Series in Data Analysis Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of lowercasing a Series with mixed case strings

What is the output of this code?

import pandas as pd
s = pd.Series(['Apple', 'Banana', 'Cherry'])
result = s.str.lower()
print(result)

Data Analysis Python

import pandas as pd
s = pd.Series(['Apple', 'Banana', 'Cherry'])
result = s.str.lower()
print(result)

A

0    aPPle
1    bANana
2    cHErry
dtype: object

B

0    apple
1    banana
2    cherry
dtype: object

C

0    APPLE
1    BANANA
2    CHERRY
dtype: object

D

0    Apple
1    Banana
2    Cherry
dtype: object

💡 Hint

The str.lower() method converts all characters in each string to lowercase.

The str.lower() method applied to a pandas Series converts every string element to lowercase. So 'Apple' becomes 'apple', 'Banana' becomes 'banana', and 'Cherry' becomes 'cherry'.

❓ data_output

intermediate

Count of strings containing a substring in a Series

Given this Series, what is the output of counting how many strings contain 'an'?

import pandas as pd
s = pd.Series(['banana', 'apple', 'mango', 'orange'])
count = s.str.contains('an').sum()
print(count)

Data Analysis Python

import pandas as pd
s = pd.Series(['banana', 'apple', 'mango', 'orange'])
count = s.str.contains('an').sum()
print(count)

A 1

B 2

C 4

D 3

💡 Hint

Check which strings have 'an' inside them.

The strings 'banana', 'mango', and 'orange' contain 'an'. So the count is 3.

🔧 Debug

advanced

Identify the error in using str.replace with regex

What error does this code raise?

import pandas as pd
s = pd.Series(['cat', 'bat', 'rat'])
result = s.str.replace('[ab]', '', regex=False)
print(result)

Data Analysis Python

import pandas as pd
s = pd.Series(['cat', 'bat', 'rat'])
result = s.str.replace('[ab]', '', regex=False)
print(result)

A TypeError: cannot use regex pattern when regex=False

B ValueError: regex argument must be True or False

C TypeError: expected string or bytes-like object

D

No error, output is:
0    ct
1    bt
2    rt
dtype: object

💡 Hint

Check the meaning of regex=False when the pattern looks like a regex.

When regex=False, the pattern is treated as a literal string, so using a regex pattern like '[ab]' causes a TypeError because it cannot interpret the pattern as a literal string.

❓ visualization

advanced

Visualize the count of string lengths in a Series

Which option shows the correct bar plot code to visualize the count of string lengths in this Series?

import pandas as pd
import matplotlib.pyplot as plt
s = pd.Series(['dog', 'cat', 'elephant', 'fox'])
lengths = s.str.len()
# Which code below plots counts of each length?

Data Analysis Python

import pandas as pd
import matplotlib.pyplot as plt
s = pd.Series(['dog', 'cat', 'elephant', 'fox'])
lengths = s.str.len()

A

lengths.value_counts().sort_index().plot(kind='bar')
plt.show()

B

lengths.plot(kind='bar')
plt.show()

C

s.str.len().plot(kind='line')
plt.show()

D

lengths.hist()
plt.show()

💡 Hint

We want counts of each length, not the lengths themselves.

value_counts() counts how many times each length appears. sort_index() orders lengths ascending. plot(kind='bar') makes a bar chart of counts.

🚀 Application

expert

Filter Series for strings starting and ending with vowels

Given this Series, which option correctly filters strings that start and end with a vowel?

import pandas as pd
s = pd.Series(['apple', 'banana', 'orange', 'umbrella', 'grape', 'avocado'])

Data Analysis Python

import pandas as pd
s = pd.Series(['apple', 'banana', 'orange', 'umbrella', 'grape', 'avocado'])

A

filtered = s[s.str.match('^[aeiou].*[aeiou]$')]
print(filtered)

B

filtered = s[s.str.contains('^[aeiou].*[aeiou]$')]
print(filtered)

C

filtered = s[s.str.startswith(('a','e','i','o','u')) & s.str.endswith(('a','e','i','o','u'))]
print(filtered)

D

filtered = s[s.str.match('^[aeiou].*[aeiou]')]
print(filtered)

💡 Hint

Check how to combine startswith and endswith for multiple letters.

Option C uses str.startswith and str.endswith with tuples of vowels, combined with & to filter strings starting and ending with vowels. str.match expects full match, so regex must have $ at end.