stri_startswith: 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, ..., opts_fixed = NULL)
stri_endswith_fixed(str, pattern, to = -1L, ..., opts_fixed = NULL)
stri_startswith_charclass(str, pattern, from = 1L)
stri_endswith_charclass(str, pattern, to = -1L)
stri_startswith_coll(str, pattern, from = 1L, ...,
  opts_collator = NULL)
stri_endswith_coll(str, pattern, to = -1L, ..., 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

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

Value

Each function returns a logical vector.

Details

Vectorized over str, pattern, and from or to.

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.

Examples

Run this code

# NOT RUN {
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)

# }