Convert ordinal to numbers

January 11, 2023

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.

>Solution :

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)}