stringi: stri_startsendswith – R documentation

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stri_startsendswith

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.

Usage

stri_startswith(str, ..., fixed, coll, charclass)

stri_endswith(str, ..., fixed, coll, charclass)

stri_startswith_fixed(
  str,
  pattern,
  from = 1L,
  negate = FALSE,
  ...,
  opts_fixed = NULL
)

stri_endswith_fixed(
  str,
  pattern,
  to = -1L,
  negate = FALSE,
  ...,
  opts_fixed = NULL
)

stri_startswith_charclass(str, pattern, from = 1L, negate = FALSE)

stri_endswith_charclass(str, pattern, to = -1L, negate = FALSE)

stri_startswith_coll(
  str,
  pattern,
  from = 1L,
  negate = FALSE,
  ...,
  opts_collator = NULL
)

stri_endswith_coll(
  str,
  pattern,
  to = -1L,
  negate = FALSE,
  ...,
  opts_collator = NULL
)

Arguments

`str`	character vector
`...`	supplementary arguments passed to the underlying functions, including additional settings for `opts_collator`, `opts_fixed`, and so on.
`pattern, fixed, coll, charclass`	character vector defining search patterns; for more details refer to stringi-search
`from`	integer vector
`negate`	single logical value; whether a no-match to a pattern is rather of interest
`to`	integer vector
`opts_collator, opts_fixed`	a named list used to tune up the search engine's settings; see `stri_opts_collator` and `stri_opts_fixed`, respectively; `NULL` for the defaults

Details

Vectorized over str, pattern, and from or to (with recycling of the elements in the shorter vector if necessary).

If pattern is empty, then the result is NA and a warning is generated.

Argument start controls the start position in str where there is a match to a pattern. to gives the end position.

Indexes given by from or 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 from or 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 str, use stri_detect.

stri_startswith and stri_endswith are convenience functions. They call either stri_*_fixed, stri_*_coll, or 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 '^' and '$' meta-characters, see stringi-search-regex.

Value

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)

stringi

Character String Processing Facilities

v1.6.1

file LICENSE

Authors

Marek Gagolewski [aut, cre, cph] (<https://orcid.org/0000-0003-0637-6028>), Bartek Tartanus [ctb], and others (stringi source code); IBM, Unicode, Inc. and others (ICU4C source code, Unicode Character Database)

Initial release

2021-05-05