extend_letters.R

# Here's a function that allows you to specify the number of letters you want (eg. 5 would be A, B, C, D, and E), the length of the code (eg. 3 would be AAA, AAB, AAC, etc), the number of results you want (NA for all of them), and and separating character (eg. '-' would give A-A-A, A-A-B, A-A-C.)

letterCodes <- function(nletters, case = 'upper', lengthCode, nResults = NA, sep = '') {
  f <- if (case == 'upper') LETTERS else letters
  a <- expand.grid(rep(list(f[1:nletters]), lengthCode))
  a <- a[, ncol(a):1]
  a <- do.call("paste", c(a, sep = sep))
  if (is.na(nResults)) a else a[1:min(nResults, length(a))]
}