str_extract
Extract matching patterns from a string.
Vectorised over string and pattern.
Usage
str_extract(string, pattern)str_extract_all(string, pattern, simplify = FALSE)
Arguments
- string
Input vector. Either a character vector, or something coercible to one.
- pattern
Pattern to look for.
The default interpretation is a regular expression, as described in stringi::stringi-search-regex. Control options with
regex().Match a fixed string (i.e. by comparing only bytes), using
fixed(). This is fast, but approximate. Generally, for matching human text, you'll wantcoll()which respects character matching rules for the specified locale.Match character, word, line and sentence boundaries with
boundary(). An empty pattern, "", is equivalent toboundary("character").- simplify
If
FALSE, the default, returns a list of character vectors. IfTRUEreturns a character matrix.
Value
A character vector.
See Also
str_match() to extract matched groups;
stringi::stri_extract() for the underlying implementation.
Examples
# NOT RUN {
shopping_list <- c("apples x4", "bag of flour", "bag of sugar", "milk x2")
str_extract(shopping_list, "\\d")
str_extract(shopping_list, "[a-z]+")
str_extract(shopping_list, "[a-z]{1,4}")
str_extract(shopping_list, "\\b[a-z]{1,4}\\b")
# Extract all matches
str_extract_all(shopping_list, "[a-z]+")
str_extract_all(shopping_list, "\\b[a-z]+\\b")
str_extract_all(shopping_list, "\\d")
# Simplify results into character matrix
str_extract_all(shopping_list, "\\b[a-z]+\\b", simplify = TRUE)
str_extract_all(shopping_list, "\\d", simplify = TRUE)
# Extract all words
str_extract_all("This is, suprisingly, a sentence.", boundary("word"))
# }
Community examples
shopping_list <- c("apples x4", "bag of flour", "bag of sugar", "milk x2") str_extract(shopping_list, "\d") str_extract(shopping_list, "[a-z]+") str_extract(shopping_list, "[a-z]{1,4}") str_extract(shopping_list, "\b[a-z]{1,4}\b")
# NOT RUN { shopping_list <- c("apples x4", "bag of flour", "bag of sugar", "milk x2") str_extract(shopping_list, "\\d") str_extract(shopping_list, "[a-z]+") str_extract(shopping_list, "[a-z]{1,4}") str_extract(shopping_list, "\\b[a-z]{1,4}\\b") # Extract all matches str_extract_all(shopping_list, "[a-z]+") str_extract_all(shopping_list, "\\b[a-z]+\\b") str_extract_all(shopping_list, "\\d") # Simplify results into character matrix str_extract_all(shopping_list, "\\b[a-z]+\\b", simplify = TRUE) str_extract_all(shopping_list, "\\d", simplify = TRUE) # Extract all words str_extract_all("This is, suprisingly, a sentence.", boundary("word")) # }