nc (version 2025.3.24)

group: Capture group

Description

Create a capture group (named column in output). In the vast majority of patterns R arguments can/should be used to specify names, e.g. list(name=pattern). This is a helper function which is useful for programmatically creating group names (see example for a typical use case).

Usage

group(name, ...)

Value

Named list.

Arguments

name

Column name in output.

...

Regex pattern(s).

Author

Toby Hocking <[e-mail]> [aut, cre]

Examples

## Three ways to create a group named data which matches zero or
## more non-newline characters.
str(list(data=".*"))
str(nc::group("data", ".*"))
g.name <- "data"
str(nc::group(g.name, ".*"))

## Data downloaded from
## https://en.wikipedia.org/wiki/Hindu%E2%80%93Arabic_numeral_system
numerals <- system.file(
  "extdata", "Hindu-Arabic-numerals.txt.gz", package="nc")

## Use engine="ICU" for unicode character classes
## http://userguide.icu-project.org/strings/regexp e.g. match any
## character with a numeric value of 2 (including japanese etc).
if(requireNamespace("stringi"))
  nc::capture_all_str(
  numerals,
  " ",
  two="[\\p{numeric_value=2}]",
  " ",
  engine="ICU")

## Create a table of numerals with script names.
digits.pattern <- list()
for(digit in 0:9){
  digits.pattern[[length(digits.pattern)+1]] <- list(
    "[|]",
    nc::group(paste(digit), "[^{|]+"),
    "[|]")
}
nc::capture_all_str(
  numerals,
  "\n",
  digits.pattern,
  "[|]",
  " *",
  "\\[\\[",
  name="[^\\]|]+")