R/str_detect.R

In stringstatic: Dependency-Free String Operations

#' Detect the presence or absence of a pattern in a string
#'
#' Dependency-free drop-in alternative for `stringr::str_detect()`.
#'
#' @source Adapted from the [stringr](https://stringr.tidyverse.org/) package.
#'
#' @param string Input vector.
#'   Either a character vector, or something coercible to one.
#'
#' @param pattern Pattern to look for.
#'
#'   The default interpretation is a regular expression,
#'   as described in [base::regex].
#'   Control options with [regex()].
#'
#'   Match a fixed string (i.e. by comparing only bytes), using [fixed()].
#'   This is fast, but approximate.
#'
#' @param negate If `TRUE`, return non-matching elements.
#'
#' @return A logical vector.
#' @export
#' @staticexport
str_detect <- function(string, pattern, negate = FALSE) {
	if (length(string) == 0 || length(pattern) == 0) return(logical(0))

	is_fixed <- inherits(pattern, "stringr_fixed")

	indices <- Vectorize(grep, c("pattern", "x"), USE.NAMES = FALSE)(
		pattern,
		x = string,
		perl = !is_fixed,
		fixed = is_fixed,
		invert = negate
	)

	result <- as.logical(lengths(indices))
	result[is.na(string)] <- NA
	result
}

#' Detect the presence or absence of a pattern at the beginning of a string
#'
#' Dependency-free drop-in alternative for `stringr::str_starts()`.
#'
#' @param string Input vector.
#'   Either a character vector, or something coercible to one.
#'
#' @param pattern Pattern to look for.
#'
#'   The default interpretation is a regular expression,
#'   as described in [base::regex].
#'   Control options with [regex()].
#'
#'   Match a fixed string (i.e. by comparing only bytes), using [fixed()].
#'   This is fast, but approximate.
#'
#' @param negate If `TRUE`, return non-matching elements.
#'
#' @return A logical vector.
#' @export
#' @staticexport
str_starts <- function(string, pattern, negate = FALSE) {
	if (length(string) == 0 || length(pattern) == 0) return(logical(0))

	is_fixed <- inherits(pattern, "stringr_fixed")

	indices <- Vectorize(grep, c("pattern", "x"), USE.NAMES = FALSE)(
		paste0("^(", pattern, ")"),
		x = string,
		perl = !is_fixed,
		fixed = is_fixed,
		invert = negate
	)

	result <- as.logical(lengths(indices))
	result[is.na(string)] <- NA
	result
}

#' Detect the presence or absence of a pattern at the end of a string
#'
#' Dependency-free drop-in alternative for `stringr::str_ends()`.
#'
#' @source Adapted from the [stringr](https://stringr.tidyverse.org/) package.
#'
#' @param string Input vector.
#'   Either a character vector, or something coercible to one.
#'
#' @param pattern Pattern to look for.
#'
#'   The default interpretation is a regular expression,
#'   as described in [base::regex].
#'   Control options with [regex()].
#'
#'   Match a fixed string (i.e. by comparing only bytes), using [fixed()].
#'   This is fast, but approximate.
#'
#' @param negate If `TRUE`, return non-matching elements.
#'
#' @return A logical vector.
#' @export
#' @staticexport
str_ends <- function(string, pattern, negate = FALSE) {
	if (length(string) == 0 || length(pattern) == 0) return(logical(0))

	is_fixed <- inherits(pattern, "stringr_fixed")

	indices <- grep <- Vectorize(grep, c("pattern", "x"), USE.NAMES = FALSE)(
		paste0("(", pattern, ")$"),
		x = string,
		perl = !is_fixed,
		fixed = is_fixed,
		invert = negate
	)

	result <- as.logical(lengths(indices))
	result[is.na(string)] <- NA
	result
}