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 (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.

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)

# }