R/getCommonPrefix.R

In HenrikBengtsson/R.utils: Various Programming Utilities

 getCommonPrefix <- function(strs, suffix=FALSE, ...) {
  # Split strings into character vectors
  nchars <- sapply(strs, FUN=nchar)
  chars <- strsplit(strs, split="")

  # Asked for the suffix?
  if (suffix) {
    chars <- lapply(chars, FUN=rev)
  }

  # Put the characters into a matrix
  naValue <- NA_character_
  data <- matrix(naValue, nrow=length(chars), ncol=max(nchars))
  for (kk in seq_along(chars)) {
    cc <- seq_len(nchars[kk])
    data[kk,cc] <- chars[[kk]]
  }

  # Find first column with different characters
  count <- 0
  for (cc in seq_len(ncol(data))) {
    uchars <- unique(data[,cc])
    if (length(uchars) > 1)
      break
    count <- cc
  }

  # The common prefix as a character vector
  prefix <- chars[[1]][seq_len(count)]

  # Asked for the suffix?
  if (suffix) {
    prefix <- rev(prefix)
  }

  # The common prefix as a character string
  prefix <- paste(prefix, collapse="")

  prefix
} # getCommonPrefix()