How to Use str_extract in R: Extract Text with Patterns

In R, use str_extract() from the stringr package to extract the first substring that matches a pattern from a string. Provide the string and a regular expression pattern as arguments, and it returns the matched text or NA if no match is found.

Syntax

The basic syntax of str_extract() is:

• string: The input character vector where you want to find matches.
• pattern: A regular expression pattern describing the text to extract.

The function returns the first match found in each string or NA if no match exists.

r

str_extract(string, pattern)

Example

This example shows how to extract the first number from each string in a vector using str_extract().

r

library(stringr)

texts <- c("Order 1234", "No number here", "ID: 5678 and 91011")

numbers <- str_extract(texts, "\\d+")
print(numbers)

Output

[1] "1234" NA "5678"

Common Pitfalls

Common mistakes include:

• Not loading the stringr package before using str_extract().
• Using incorrect regular expression syntax, like forgetting to escape special characters.
• Expecting str_extract() to return all matches instead of only the first match (use str_extract_all() for all matches).

r

library(stringr)

# Wrong: forgetting to escape backslash
# str_extract("Price: $100", "\\d+") # Correct
# str_extract("Price: $100", "\d+") # Incorrect, will cause error

# Correct usage
str_extract("Price: $100", "\\d+")

Output

[1] "100"

Quick Reference

Function	Description
str_extract(string, pattern)	Extracts first match of pattern from string
str_extract_all(string, pattern)	Extracts all matches of pattern from string
stringr::str_detect(string, pattern)	Checks if pattern exists in string (TRUE/FALSE)
stringr::str_replace(string, pattern, replacement)	Replaces first match of pattern with replacement

Key Takeaways

Use str_extract() to get the first matching text from a string using a regex pattern.

Always load the stringr package with library(stringr) before using str_extract().

Escape special characters in regex patterns properly with double backslashes (\\).

str_extract() returns NA if no match is found in the string.

For all matches, use str_extract_all() instead of str_extract().