R/search_startsendswith_4.R

In stringi: Fast and Portable Character String Processing Facilities

# kate: default-dictionary en_US

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#' @title
#' Determine if the Start or End of a String Matches a Pattern
#'
#' @description
#' These functions check if a string starts or ends with a match
#' to a given pattern. Also, it is possible to check if there is a match
#' at a specific position.
#'
#' @details
#' Vectorized over \code{str}, \code{pattern},
#' and \code{from} or \code{to} (with recycling
#' of the elements in the shorter vector if necessary).
#'
#' If \code{pattern} is empty, then the result is \code{NA}
#' and a warning is generated.
#'
#' Argument \code{start} controls the start position in \code{str}
#' where there is a match to a \code{pattern}.
#' \code{to} gives the end position.
#'
#' Indexes given by \code{from} or \code{to} are of course 1-based,
#' i.e., an index 1 denotes the first character
#' in a string. This gives a typical R look-and-feel.
#'
#' For negative indexes in \code{from} or \code{to}, counting starts
#' at the end of the string. For instance, index -1 denotes the last code point
#' in the string.
#'
#' If you wish to test for a pattern match at an arbitrary
#' position in \code{str}, use \code{\link{stri_detect}}.
#'
#' \code{stri_startswith} and \code{stri_endswith} are convenience functions.
#' They call either \code{stri_*_fixed}, \code{stri_*_coll},
#' or \code{stri_*_charclass}, depending on the argument used.
#' Relying on these underlying functions directly will make your code run
#' slightly faster.
#'
#' Note that testing for a pattern match at the start or end of a string
#' has not been implemented separately for regex patterns.
#' For that you may use the '\code{^}' and '\code{$}' meta-characters,
#' see \link{stringi-search-regex}.
#'
#' @param str character vector
#' @param pattern,fixed,coll,charclass character vector defining search patterns;
#' for more details refer to \link{stringi-search}
#' @param from integer vector
#' @param to integer vector
#' @param negate single logical value; whether a no-match to a pattern
#'     is rather of interest
#' @param opts_collator,opts_fixed a named list used to tune up
#' the search engine's settings; see \code{\link{stri_opts_collator}}
#' and \code{\link{stri_opts_fixed}}, respectively; \code{NULL}
#' for the defaults
#' @param ... supplementary arguments passed to the underlying functions,
#' including additional settings for \code{opts_collator}, \code{opts_fixed},
#' and so on.
#'
#' @return Each function returns a logical vector.
#'
#'
#' @examples
#' stri_startswith_charclass(' trim me! ', '\\p{WSpace}')
#' stri_startswith_fixed(c('a1', 'a2', 'b3', 'a4', 'c5'), 'a')
#' stri_detect_regex(c('a1', 'a2', 'b3', 'a4', 'c5'), '^a')
#' stri_startswith_fixed('ababa', 'ba')
#' stri_startswith_fixed('ababa', 'ba', from=2)
#' stri_startswith_coll(c('a1', 'A2', 'b3', 'A4', 'C5'), 'a', strength=1)
#' pat <- stri_paste('\u0635\u0644\u0649 \u0627\u0644\u0644\u0647 ',
#'                   '\u0639\u0644\u064a\u0647 \u0648\u0633\u0644\u0645XYZ')
#' stri_endswith_coll('\ufdfa\ufdfa\ufdfaXYZ', pat, strength=1)
#'
#' @family search_detect
#' @export
#' @rdname stri_startsendswith
stri_startswith <- function(str, ..., fixed, coll, charclass)
{
    providedarg <- c(
        fixed = !missing(fixed),
        coll = !missing(coll),
        charclass = !missing(charclass))

    if (sum(providedarg) != 1)
        stop("you have to specify either `fixed`, `coll`, or `charclass`")

    if (providedarg["fixed"])
        stri_startswith_fixed(str, fixed, ...)
    else if (providedarg["coll"])
        stri_startswith_coll(str, coll, ...)
    else if (providedarg["charclass"])
        stri_startswith_charclass(str, charclass, ...)
}


#' @export
#' @rdname stri_startsendswith
stri_endswith <- function(str, ..., fixed, coll, charclass)
{
    providedarg <- c(
        fixed = !missing(fixed),
        coll = !missing(coll),
        charclass = !missing(charclass))

    if (sum(providedarg) != 1)
        stop("you have to specify either `fixed`, `coll`, or `charclass`")

    if (providedarg["fixed"])
        stri_endswith_fixed(str, fixed, ...)
    else if (providedarg["coll"])
        stri_endswith_coll(str, coll, ...)
    else if (providedarg["charclass"])
        stri_endswith_charclass(str, charclass, ...)
}


#' @export
#' @rdname stri_startsendswith
stri_startswith_fixed <- function(str, pattern, from = 1L,
    negate = FALSE, ..., opts_fixed = NULL)
{
    if (!missing(...))
        opts_fixed <- do.call(stri_opts_fixed, as.list(c(opts_fixed, ...)))
    .Call(C_stri_startswith_fixed, str, pattern, from, negate, opts_fixed)
}


#' @export
#' @rdname stri_startsendswith
stri_endswith_fixed <- function(str, pattern, to = -1L,
    negate = FALSE, ..., opts_fixed = NULL)
{
    if (!missing(...))
        opts_fixed <- do.call(stri_opts_fixed, as.list(c(opts_fixed, ...)))
    .Call(C_stri_endswith_fixed, str, pattern, to, negate, opts_fixed)
}


#' @export
#' @rdname stri_startsendswith
stri_startswith_charclass <- function(str, pattern, from = 1L, negate = FALSE)
{
    .Call(C_stri_startswith_charclass, str, pattern, from, negate)
}


#' @export
#' @rdname stri_startsendswith
stri_endswith_charclass <- function(str, pattern, to = -1L, negate = FALSE)
{
    .Call(C_stri_endswith_charclass, str, pattern, to, negate)
}


#' @export
#' @rdname stri_startsendswith
stri_startswith_coll <- function(str, pattern, from = 1L,
    negate = FALSE, ..., opts_collator = NULL)
{
    if (!missing(...))
        opts_collator <- do.call(stri_opts_collator, as.list(c(opts_collator, ...)))
    .Call(C_stri_startswith_coll, str, pattern, from, negate, opts_collator)
}


#' @export
#' @rdname stri_startsendswith
stri_endswith_coll <- function(str, pattern, to = -1L,
    negate = FALSE, ..., opts_collator = NULL)
{
    if (!missing(...))
        opts_collator <- do.call(stri_opts_collator, as.list(c(opts_collator, ...)))
    .Call(C_stri_endswith_coll, str, pattern, to, negate, opts_collator)
}