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################ numbers2words ###################
##################################################
numbers2words <- function(x, billion = c("US", "UK"), and = if (billion == "US") "" else "and") {
   ## Description:
   ##   Converts a number into its corresponding words in English
   ##   == THIS FUNCTION WAS PUBLISHED IN: R-News, vol 5, iss 1, May 2005, pp. 51
   ##   == Original author: John Fox
   ##   == Department of Sociology
   ##   == McMaster University
   ##   == Hamilton, Ontario
   ##   == Canada L8S 4M4
   ##   == 905-525-9140x23604
   ##   == http://socserv.mcmaster.ca/jfox 
   ##   == http://cran.csiro.au/doc/Rnews/Rnews_2005-1.pdf
   ##   == http://finzi.psych.upenn.edu/R/Rhelp02a/archive/46843.html
   ## Usage:
   ##   numbers2words(number, billion-word, and-or-not)
   ## Arguments:
   ##   x: number
   ##   billion: follow either US or UK usage rules
   ##   and: follows the choice set in billion arg
   ## Value:
   ##   Dataframe with the following columns:
   ##   $ sampleid        : chr
   #
   billion <- match.arg(billion)
   trim <- function(text) {
      gsub("(^\ *)|((\ *|-|,\ zero|-zero)$)", "", text)
   }
   makeNumber <- function(x) as.numeric(paste(x, collapse = ""))
   makeDigits <- function(x) strsplit(as.character(x), "")[[1]]
   helper <- function(x) {
      negative <- x < 0
      x <- abs(x)
      digits <- makeDigits(x)
      nDigits <- length(digits)
      result <- if (nDigits == 1) as.vector(ones[digits])
      else if (nDigits == 2)
      if (x <= 19) as.vector(teens[digits[2]])
      else trim(paste(tens[digits[1]], "-", ones[digits[2]], sep=""))
      else if (nDigits == 3) {
         tail <- makeNumber(digits[2:3])
         if (tail == 0) paste(ones[digits[1]], "hundred")
         else trim(paste(ones[digits[1]], trim(paste("hundred", and)),
         helper(tail)))
      } else {
         nSuffix <- ((nDigits + 2) %/% 3) - 1
         if (nSuffix > length(suffixes) || nDigits > 15)
         stop(paste(x, "is too large!"))
         pick <- 1:(nDigits - 3 * nSuffix)
         trim(paste(helper(makeNumber(digits[pick])), suffixes[nSuffix], helper(makeNumber(digits[-pick]))))
      }
      if (billion == "UK") {
         words <- strsplit(result, " ")[[1]]
         if (length(grep("million,", words)) > 1)
         result <- sub(" million, ", ", ", result)
      }
      if (negative) paste("minus", result) else result
   }
   opts <- options(scipen = 100)
   on.exit(options(opts))
   ones <- c("zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine")
   teens <- c("ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", " seventeen", "eighteen", "nineteen")
   names(ones) <- names(teens) <- 0:9
   tens <- c("twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety")
   names(tens) <- 2:9
   suffixes <- if (billion == "US") {
         c("thousand,", "million,", "billion,", "trillion,")
      } else {
         c("thousand,", "million,", "thousand million,", "billion,")
      }
   x <- round(x)
   if (length(x) > 1) sapply(x, helper) else helper(x)
}