Regular expressions in R in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a regular expression (regex) in R?

A regular expression is a pattern of characters used to find or match text in strings. In R, regex helps search, replace, or split text based on these patterns.

beginner

Which R function is commonly used to check if a pattern exists in a string?

The grepl() function returns TRUE if the pattern is found in the string, otherwise FALSE.

intermediate

How do you extract matched text using regex in R?

Use regmatches() with gregexpr() to extract all matches of a pattern from a string.

beginner

What does the regex pattern ^abc mean?

It means the string must start with the characters 'abc'. The caret ^ anchors the match to the start of the string.

intermediate

How can you replace all digits in a string with '#' in R?

Use gsub("\\\d", "#", text). Here, \\\d matches any digit, and gsub() replaces all matches.

Which function returns the positions of regex matches in a string in R?

A regmatches()

B grepl()

C gsub()

D gregexpr()

gregexpr() returns the starting positions of all matches of a pattern in a string.

What does the regex symbol \d represent in R?

A Any letter

B Any whitespace

C Any digit (0-9)

D Start of string

\d matches any digit from 0 to 9.

Which function would you use to replace text matching a regex pattern in R?

A gsub()

B gregexpr()

C grepl()

D regexpr()

gsub() replaces all occurrences of a pattern with a replacement string.

What does the regex pattern abc$ mean?

A String ends with 'abc'

B String starts with 'abc'

C String contains 'abc' anywhere

D String has 'abc' repeated

The dollar sign $ anchors the match to the end of the string.

Which function returns TRUE or FALSE if a pattern is found in a string?

A gsub()

B grepl()

C regmatches()

D gregexpr()

grepl() returns a logical value indicating if the pattern exists.

Explain how to find and extract all occurrences of a pattern in a string using R regex functions.

Think about functions that locate positions and then extract text.

Describe how to replace all digits in a string with a specific character using regular expressions in R.

Consider the function that replaces all matches, not just the first.