nc (version 2025.3.24)

altlist: altlist

Description

Create a named list containing named patterns, useful for creating a named list of named sub-pattern groups to be used with alternatives. This function is used to implement the more user-friendly alternatives_with_shared_groups, which should be preferred.

Usage

altlist(...)

Value

Named list of patterns to be used for constructing alternatives

using with, see examples.

Arguments

...

Named patterns which will be used as sub-pattern groups in alternatives.

Author

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

Examples

## Example 1: matching dates in different formats, but always same
## type in each alternative.
subject.vec <- c("mar 17, 1983", "26 sep 2017", "17 mar 1984")
pat.list <- nc::altlist(month="[a-z]{3}", day="[0-9]{2}", year="[0-9]{4}")
pattern <- with(pat.list, nc::alternatives(
  american=list(month, " ", day, ", ", year),
  european=list(day, " ", month, " ", year)))
match.dt <- nc::capture_first_vec(subject.vec, pattern)
print(match.dt, class=TRUE)
match.dt[, data.table::as.IDate(paste0(month, day, year), format="%b%d%Y")]

## Example 2: matching dates in different formats, but with
## different types in different alternatives.
subject.vec <- c("3/17/1983", "26 sep 2017")
month2int <- c(#this approach is locale-indepdendent.
  jan=1L, feb=2L, mar=3L, apr=4L,  may=5L,  jun=6L,
  jul=7L, aug=8L, sep=9L, oct=10L, nov=11L, dec=12L)
pat.list <- nc::altlist(
  day=list("[0-9]{2}", as.integer),
  year=list("[0-9]{4}", as.integer))
pattern <- with(pat.list, nc::alternatives(
  american=list(month="[0-9]", as.integer, "/", day, "/", year),
  european=list(
    day, " ", month="[a-z]{3}", function(m)month2int[m], " ", year)))
match.dt <- nc::capture_first_vec(subject.vec, pattern)
print(match.dt, class=TRUE)