Regex operations in Pandas - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the str.contains() method do in Pandas when used with regex?

It checks each string in a Series to see if it contains a pattern defined by a regular expression, returning a Series of True or False values.

beginner

How do you use regex to extract a pattern from a Pandas Series?

Use the str.extract() method with a regex pattern. It returns a DataFrame with the matched groups.

beginner

What is the purpose of the str.replace() method with regex in Pandas?

It replaces parts of strings that match a regex pattern with a specified replacement string.

intermediate

How can you filter rows in a DataFrame where a column matches a regex pattern?

Use df[df['column'].str.contains('pattern', regex=True)] to keep rows where the pattern is found.

intermediate

What does setting na=False do in str.contains()?

It treats missing values (NaN) as False, so they don't cause errors and are excluded from matches.

Which Pandas method extracts regex groups from a Series?

A str.extract()

B str.contains()

C str.replace()

D str.match()

str.extract() pulls out matching groups from strings using regex.

What does str.contains('abc', regex=True) return?

A Replaces 'abc' with True

B A Series of strings containing 'abc'

C A DataFrame with extracted 'abc' matches

D A Series of True/False indicating if 'abc' is in each string

It returns True or False for each string depending on if 'abc' is found.

How do you replace all digits in a Series with '#' using regex?

A str.extract('\d')

B str.replace('#', '\d', regex=True)

C str.replace('\d', '#', regex=True)

D str.contains('\d')

Use str.replace() with regex pattern '\d' to replace digits.

What happens if you use str.contains() on a Series with NaN values without na=False?

A Raises an error

B Returns False for NaN values

C Ignores NaN values

D Returns True for NaN values

By default, it returns NaN for NaN values, not an error. Use na=False to treat NaN as False.

Which method would you use to check if a string starts with a pattern using regex?

A str.contains()

B str.match()

C str.extract()

D str.replace()

str.match() checks if the entire string matches a regex pattern, often used for start matches.

Explain how to filter a Pandas DataFrame column to keep only rows where the text matches a regex pattern.

Think about using a method that returns True/False for each row and then selecting rows.

Describe how to extract parts of strings from a Pandas Series using regex groups.

Focus on the method that pulls out matching parts instead of just checking presence.