R/toAsciiRegExprPattern.R

In HenrikBengtsson/R.utils: Various Programming Utilities

# Parses a regular expression and replaces sets to ASCII sets.
setMethodS3("toAsciiRegExprPattern", "character", function(pattern, ...) {
  bfr <- strsplit(pattern, split="")[[1]]
  bfr2 <- c()
  state <- "plain"
  while(length(bfr) > 0) {
    ch <- bfr[1]
    bfr <- bfr[-1]
    if (state == "plain") {
      if (ch == "[") {
        set <- c()
        state <- "set"
      } else {
        bfr2 <- c(bfr2, ch)
      }
    } else if (state == "set") {
      if (ch == "]") {
        # Expand set
        set2 <- c()
        ch <- NA
        setState <- "plain"
        while (length(set) > 0) {
          prevCh <- ch
          ch <- set[1]
          set <- set[-1]
#print(list(setState=setState, ch=ch, prevCh=prevCh))
          if (setState == "plain") {
            if (ch == "-") {
              if (is.na(prevCh)) {
                set2 <- c(set2, ch)
              } else {
                from <- prevCh
                setState <- "range"
              }
            }
          } else if (setState == "range") {
            to <- ch
            allLetters <- c(base::letters, base::LETTERS)
            if (all(c(from, to) %in% allLetters)) {
              from <- match(from, allLetters)
              to <- match(to, allLetters)
              set2 <- c(set2, allLetters[from:to])
            } else {
              set2 <- c(set2, from, "-", to)
            }
            setState <- "plain"
          }
        } # while (length(set) > 0)
        bfr2 <- c(bfr2, "[", set2, "]")
        state <- "plain"
      } else {
        set <- c(set, ch)
      }
    }
  }
  pattern <- paste(bfr2, collapse="")
  pattern
})