stringr function to concatenate vector of words separated by comma with “and” before last word

Question

I know I can easily write one, but does anyone know if stringr (or stringi) already has a function that concatenates a vector of one or more words separated by commas, but with

Answer 1

You can use the knitr::combine_words function

knitr::combine_words(letters[1:2])
# [1] "a and b"
knitr::combine_words(letters[1:3])
# [1] "a, b, and c"
knitr::combine_words(letters[1:4])
# [1] "a, b, c, and d"

Answer 2

Here's another solution :

enum <- function(x) 
  paste(c(head(x,-2), paste(tail(x,2), collapse = ", and ")), collapse = ", ")
enum(letters[1])
#> [1] "a"
enum(letters[1:2])
#> [1] "a, and b"
enum(letters[1:3])
#> [1] "a, b, and c"
enum(letters[1:4])
#> [1] "a, b, c, and d"

^{Created on 2019-05-11 by the reprex package (v0.2.1)}