altlist: altlist

In nc: Named Capture to Data Tables

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. Instead of using this function directly, most users should try alternatives_with_shared_groups which is more user-friendly and covers the most common use cases. You should only have to use altlist directly if your alternatives also have names (see examples).

Usage

altlist(...)

Arguments

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

Value

Named list of patterns to be used for constructing alternatives using with, see examples.

Author(s)

Toby Dylan Hocking

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)

nc documentation built on Sept. 1, 2023, 1:07 a.m.