modifiers: Control matching behaviour with modifier functions

In stringr: Simple, Consistent Wrappers for Common String Operations

Control matching behaviour with modifier functions

Description

Modifier functions control the meaning of the pattern argument to stringr functions:

• boundary(): Match boundaries between things.

• coll(): Compare strings using standard Unicode collation rules.

• fixed(): Compare literal bytes.

• regex() (the default): Uses ICU regular expressions.

Usage

fixed(pattern, ignore_case = FALSE)

coll(pattern, ignore_case = FALSE, locale = "en", ...)

regex(
  pattern,
  ignore_case = FALSE,
  multiline = FALSE,
  comments = FALSE,
  dotall = FALSE,
  ...
)

boundary(
  type = c("character", "line_break", "sentence", "word"),
  skip_word_none = NA,
  ...
)

Arguments

pattern	Pattern to modify behaviour.
ignore_case	Should case differences be ignored in the match? For fixed(), this uses a simple algorithm which assumes a one-to-one mapping between upper and lower case letters.
locale	Locale to use for comparisons. See stringi::stri_locale_list() for all possible options. Defaults to "en" (English) to ensure that default behaviour is consistent across platforms.
...	Other less frequently used arguments passed on to stringi::stri_opts_collator(), stringi::stri_opts_regex(), or stringi::stri_opts_brkiter()
multiline	If TRUE, $ and ^ match the beginning and end of each line. If FALSE, the default, only match the start and end of the input.
comments	If TRUE, white space and comments beginning with ⁠#⁠ are ignored. Escape literal spaces with ⁠\\ ⁠.
dotall	If TRUE, . will also match line terminators.
type	Boundary type to detect. character Every character is a boundary. line_break Boundaries are places where it is acceptable to have a line break in the current locale. sentence The beginnings and ends of sentences are boundaries, using intelligent rules to avoid counting abbreviations (details). word The beginnings and ends of words are boundaries.
skip_word_none	Ignore "words" that don't contain any characters or numbers - i.e. punctuation. Default NA will skip such "words" only when splitting on word boundaries.

Value

A stringr modifier object, i.e. a character vector with parent S3 class stringr_pattern.

Examples

pattern <- "a.b"
strings <- c("abb", "a.b")
str_detect(strings, pattern)
str_detect(strings, fixed(pattern))
str_detect(strings, coll(pattern))

# coll() is useful for locale-aware case-insensitive matching
i <- c("I", "\u0130", "i")
i
str_detect(i, fixed("i", TRUE))
str_detect(i, coll("i", TRUE))
str_detect(i, coll("i", TRUE, locale = "tr"))

# Word boundaries
words <- c("These are   some words.")
str_count(words, boundary("word"))
str_split(words, " ")[[1]]
str_split(words, boundary("word"))[[1]]

# Regular expression variations
str_extract_all("The Cat in the Hat", "[a-z]+")
str_extract_all("The Cat in the Hat", regex("[a-z]+", TRUE))

str_extract_all("a\nb\nc", "^.")
str_extract_all("a\nb\nc", regex("^.", multiline = TRUE))

str_extract_all("a\nb\nc", "a.")
str_extract_all("a\nb\nc", regex("a.", dotall = TRUE))

stringr documentation built on Nov. 15, 2023, 1:08 a.m.