stri_extract: Extract Occurrences of a Pattern

In stringi: Character String Processing Facilities

Description

These functions extract all substrings matching a given pattern.

stri_extract_all_* extracts all the matches. stri_extract_first_* and stri_extract_last_* yield the first or the last matches, respectively.

Usage

stri_extract_all(str, ..., regex, fixed, coll, charclass)

stri_extract_first(str, ..., regex, fixed, coll, charclass)

stri_extract_last(str, ..., regex, fixed, coll, charclass)

stri_extract(
  str,
  ...,
  regex,
  fixed,
  coll,
  charclass,
  mode = c("first", "all", "last")
)

stri_extract_all_charclass(
  str,
  pattern,
  merge = TRUE,
  simplify = FALSE,
  omit_no_match = FALSE
)

stri_extract_first_charclass(str, pattern)

stri_extract_last_charclass(str, pattern)

stri_extract_all_coll(
  str,
  pattern,
  simplify = FALSE,
  omit_no_match = FALSE,
  ...,
  opts_collator = NULL
)

stri_extract_first_coll(str, pattern, ..., opts_collator = NULL)

stri_extract_last_coll(str, pattern, ..., opts_collator = NULL)

stri_extract_all_regex(
  str,
  pattern,
  simplify = FALSE,
  omit_no_match = FALSE,
  ...,
  opts_regex = NULL
)

stri_extract_first_regex(str, pattern, ..., opts_regex = NULL)

stri_extract_last_regex(str, pattern, ..., opts_regex = NULL)

stri_extract_all_fixed(
  str,
  pattern,
  simplify = FALSE,
  omit_no_match = FALSE,
  ...,
  opts_fixed = NULL
)

stri_extract_first_fixed(str, pattern, ..., opts_fixed = NULL)

stri_extract_last_fixed(str, pattern, ..., opts_fixed = NULL)

Arguments

str	character vector; strings to search in
...	supplementary arguments passed to the underlying functions, including additional settings for opts_collator, opts_regex, and so on
mode	single string; one of: 'first' (the default), 'all', 'last'
pattern, regex, fixed, coll, charclass	character vector; search patterns; for more details refer to stringi-search
merge	single logical value; indicates whether consecutive pattern matches will be merged into one string; stri_extract_all_charclass only
simplify	single logical value; if TRUE or NA, then a character matrix is returned; otherwise (the default), a list of character vectors is given, see Value; stri_extract_all_* only
omit_no_match	single logical value; if FALSE, then a missing value will indicate that there was no match; stri_extract_all_* only
opts_collator, opts_fixed, opts_regex	a named list to tune up the search engine's settings; see stri_opts_collator, stri_opts_fixed, and stri_opts_regex, respectively; NULL for the defaults

Details

Vectorized over str and pattern (with recycling of the elements in the shorter vector if necessary). This allows to, for instance, search for one pattern in each given string, search for each pattern in one given string, and search for the i-th pattern within the i-th string.

Check out stri_match for the extraction of matches to individual regex capture groups.

stri_extract, stri_extract_all, stri_extract_first, and stri_extract_last are convenience functions. They merely call stri_extract_*_*, depending on the arguments used.

Value

For stri_extract_all*, if simplify=FALSE (the default), then a list of character vectors is returned. Each list element represents the results of a different search scenario. If a pattern is not found and omit_no_match=FALSE, then a character vector of length 1 with single NA value will be generated.

Otherwise, i.e., if simplify is not FALSE, then stri_list2matrix with byrow=TRUE argument is called on the resulting object. In such a case, the function yields a character matrix with an appropriate number of rows (according to the length of str, pattern, etc.). Note that stri_list2matrix's fill argument is set either to an empty string or NA, depending on whether simplify is TRUE or NA, respectively.

stri_extract_first* and stri_extract_last* return a character vector. A NA element indicates a no-match.

Note that stri_extract_last_regex searches from start to end, but skips overlapping matches, see the example below.

Author(s)

Marek Gagolewski and other contributors

See Also

The official online manual of stringi at https://stringi.gagolewski.com/

Other search_extract: about_search, stri_extract_all_boundaries(), stri_match_all()

Examples

stri_extract_all('XaaaaX', regex=c('\\p{Ll}', '\\p{Ll}+', '\\p{Ll}{2,3}', '\\p{Ll}{2,3}?'))
stri_extract_all('Bartolini', coll='i')
stri_extract_all('stringi is so good!', charclass='\\p{Zs}') # all white-spaces

stri_extract_all_charclass(c('AbcdeFgHijK', 'abc', 'ABC'), '\\p{Ll}')
stri_extract_all_charclass(c('AbcdeFgHijK', 'abc', 'ABC'), '\\p{Ll}', merge=FALSE)
stri_extract_first_charclass('AaBbCc', '\\p{Ll}')
stri_extract_last_charclass('AaBbCc', '\\p{Ll}')

## Not run: 
# emoji support available since ICU 57
stri_extract_all_charclass(stri_enc_fromutf32(32:55200), '\\p{EMOJI}')

## End(Not run)

stri_extract_all_coll(c('AaaaaaaA', 'AAAA'), 'a')
stri_extract_first_coll(c('Yy\u00FD', 'AAA'), 'y', strength=2, locale='sk_SK')
stri_extract_last_coll(c('Yy\u00FD', 'AAA'), 'y',  strength=1, locale='sk_SK')

stri_extract_all_regex('XaaaaX', c('\\p{Ll}', '\\p{Ll}+', '\\p{Ll}{2,3}', '\\p{Ll}{2,3}?'))
stri_extract_first_regex('XaaaaX', c('\\p{Ll}', '\\p{Ll}+', '\\p{Ll}{2,3}', '\\p{Ll}{2,3}?'))
stri_extract_last_regex('XaaaaX', c('\\p{Ll}', '\\p{Ll}+', '\\p{Ll}{2,3}', '\\p{Ll}{2,3}?'))

stri_list2matrix(stri_extract_all_regex('XaaaaX', c('\\p{Ll}', '\\p{Ll}+')))
stri_extract_all_regex('XaaaaX', c('\\p{Ll}', '\\p{Ll}+'), simplify=TRUE)
stri_extract_all_regex('XaaaaX', c('\\p{Ll}', '\\p{Ll}+'), simplify=NA)

stri_extract_all_fixed('abaBAba', 'Aba', case_insensitive=TRUE)
stri_extract_all_fixed('abaBAba', 'Aba', case_insensitive=TRUE, overlap=TRUE)

# Searching for the last occurrence:
# Note the difference - regex searches left to right, with no overlaps.
stri_extract_last_fixed("agAGA", "aga", case_insensitive=TRUE)
stri_extract_last_regex("agAGA", "aga", case_insensitive=TRUE)

stringi documentation built on May 17, 2021, 9:07 a.m.