Convert ordinal to numbers-CodePudding

Is there a built-in way to convert ordinal numbers to numeric vectors?

ordinal <- c("First", "Third", "Second")
ordinal_to_numeric(ordinal)
#[1] 1 3 2

ordinal2 <- c("1st", "4th", "2nd")
ordinal_to_numeric(ordinal)
#[1] 1 4 2

One could indeed create a dictionary, but this could be cumbersome easily.

CodePudding user response：

Not exactly built-in, but you can use Ritchie Sacramento's suggestion of the english package. You first make a long string of the ordinal values in words. Then you find the place of your words in these ordered list of ordinal values:

library(english)
ordinal <- c("First", "Third", "Second")
o <- ordinal(1:1000)
match(tolower(ordinal), o)
#> [1] 1 3 2

The second, as Ritchie suggests, is less complicated. I used a slightly different method, but ultimately it does the same thing.

ordinal2 <- c("1st", "4th", "2nd")
as.numeric(stringr::str_extract(ordinal2, "\\d "))
#> [1] 1 4 2

^{Created on 2023-01-11 by the reprex package (v2.0.1)}

You could even put them together in a single function:

ordinal_to_numeric <- function(x, max_ord=1000){
  if(any(grepl("\\d", x))){
    as.numeric(stringr::str_extract(x, "\\d "))
  }else{
    require(english, quietly = TRUE)
    o <- ordinal(seq(1,max_ord, by=1))
    match(tolower(x), o)
  }
}
ordinal <- c("First", "Third", "Second")
ordinal_to_numeric(ordinal)
#> [1] 1 3 2

ordinal2 <- c("1st", "4th", "2nd")
ordinal_to_numeric(ordinal2)
#> [1] 1 4 2

^{Created on 2023-01-11 by the reprex package (v2.0.1)}

CodePudding user response：

I’m late to the party and @DaveArmstrong’s solution is definitely simpler, but here’s a slightly more generic solution that first converts ordinals to cardinals, then passes these to nombre::uncardinal() for conversion to numeric. The str_replace_all() vector for ordinal -> cardinal conversion is based on source code for nombre::ordinal().

library(stringr)
library(nombre)

ordinal_to_numeric <- function(x) {
  w_word_stem <- function(x) {
    x |>
    str_to_lower() |>
    str_remove("st$|nd$|rd$|th$") |>
    str_replace_all(c(
      "fir$" = "one",
      "seco$" = "two",
      "thi$" = "three",
      "f$" = "ve",
      "eigh$" = "eight",
      "nin$" = "nine",
      "ie$" = "y"
    )) |>
    uncardinal()
  }
  w_num_stem <- function(x) {
    x |>
      str_extract("^-?\\d ") |>
      as.numeric()
  }
  out <- suppressWarnings(ifelse(
    str_starts(x, "-?\\d"), 
    w_num_stem(x),
    w_word_stem(x)
  ))
  if (any(is.na(out) & !is.na(x))) {
    warning("Conversion failed for some inputs")
  }
  out
}

ordinal <- c("First", "Third", "Second", "Five Hundred Thirty Eighth", "Negative Twenty-Third")
ordinal_to_numeric(ordinal)
# 1   3   2 538 -23

ordinal2 <- c("1st", "4th", "2nd", "538th", "-23rd")
ordinal_to_numeric(ordinal2)
# 1   4   2 538 -23