str_detect
Detect the presence or absence of a pattern in a string.
Vectorised over string and pattern.
Equivalent to grepl(pattern, x).
See str_which() for an equivalent to grep(pattern, x).
Usage
str_detect(string, pattern, negate = 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").- negate
If
TRUE, return non-matching elements.
Value
A logical vector.
See Also
stringi::stri_detect() which this function wraps,
str_subset() for a convenient wrapper around
x[str_detect(x, pattern)]
Examples
# NOT RUN {
fruit <- c("apple", "banana", "pear", "pinapple")
str_detect(fruit, "a")
str_detect(fruit, "^a")
str_detect(fruit, "a$")
str_detect(fruit, "b")
str_detect(fruit, "[aeiou]")
# Also vectorised over pattern
str_detect("aecfg", letters)
# Returns TRUE if the pattern do NOT match
str_detect(fruit, "^p", negate = TRUE)
# }
Community examples
## Alternatives ``` ex01 = data.frame(fruits = c("apple", "apple", "orange", "banana", "orange", "orange", "banana", "apple"), taste = c("sweet", "tarty", "tangy", "sweet", "tangy", "tangy", "sweet", "sweet"), qty = c(3, 2, 3, 2, 4, 1, 6, 2)) ``` To find tangy *and* sweet fruits: ``` ex01[str_detect(ex01$taste, "(tan)|(swe)"), ] ```
## Alternatives ``` ex01 = data.frame(fruits = c("apple", "apple", "orange", "banana", "orange", "orange", "banana", "apple"), taste = c("sweet", "tarty", "tangy", "sweet", "tangy", "tangy", "sweet", "sweet"), qty = c(3, 2, 3, 2, 4, 1, 6, 2)) ``` To find tangy *and* sweet fruits: ``` ex01[str_detect(ex01$taste, "(tan)|(swe)"), ] ```
comparison with `grepl`: `str_detect` behaves the same as `grepl` if we use only 2 first arguments (i.e. if we keep all optional parameters as default for `grepl`). These 2 first arguments are switched however. ```r fruit <- c("apple", "banana", "pear", "pinapple") # [1] TRUE identical(str_detect(fruit, "a"), grepl("a",fruit)) # [1] TRUE identical(str_detect(fruit, "^a"), grepl("^a",fruit)) # [1] TRUE identical(str_detect(fruit, "a$"), grepl("a$",fruit)) # [1] TRUE identical(str_detect(fruit, "b"), grepl("b",fruit)) # [1] TRUE identical(str_detect(fruit, "[aeiou]"), grepl("[aeiou]",fruit)) # [1] TRUE ``` An additional feature of `str_detect` is that it is vectorized over the `pattern` argument: ``` str_detect("aecfg", letters) grepl(letters,"aecfg") # [1] TRUE # Warning message: # In grepl(letters, "aecfg") : # argument 'pattern' has length > 1 and only the first element will be used identical(str_detect("aecfg", letters), Vectorize(grepl,"pattern", USE.NAMES=FALSE)(letters,"aecfg")) # [1] TRUE ```
ex01 = data.frame(fruits = c("apple", "apple", "orange", "banana", "orange", "orange", "banana", "apple"), taste = c("sweet", "tarty", "tangy", "sweet", "tangy", "tangy", "sweet", "sweet"), qty = c(3, 2, 3, 2, 4, 1, 6, 2)) #### to select using string matches - the sweet ones ex01[str_detect(ex01$taste, "swe"), ]
ex01 = data.frame(fruits = c("apple", "apple", "orange", "banana", "orange", "orange", "banana", "apple"), taste = c("sweet", "tarty", "tangy", "sweet", "tangy", "tangy", "sweet", "sweet"), qty = c(3, 2, 3, 2, 4, 1, 6, 2)) #### to select using string matches - the sweet ones ex01[str_detect(ex01$taste, "swe"), ]
ex01 = data.frame(fruits = c("apple", "apple", "orange", "banana", "orange", "orange", "banana", "apple"), taste = c("sweet", "tarty", "tangy", "sweet", "tangy", "tangy", "sweet", "sweet"), qty = c(3, 2, 3, 2, 4, 1, 6, 2)) #### to select using string matches - the sweet ones ex01[str_detect(ex01$taste, "swe"), ]