R/lex.R

In coolbutuseless/svgparser: Read SVG as Grobs and Data Frames

# nocov start

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#' Break a string into labelled tokens based upon a set of patterns
#'
#' @param text a single character string
#' @param regexes a named vector of regex strings.  Each string represents
#'                a regex to match a token, and the name of the string is the
#'                label for the token.  Each regex can contain an explicit
#'                captured group using the standard \code{()} brackets. If a regex
#'                doesn't not define a captured group then the entire regex will
#'                be captured. The regexes
#'                will be processed in order such that an early match takes
#'                 precedence over any later match.
#' @param verbose print more information about the matching process. default: FALSE
#'
#' @return a named character vector with the names representing the token type
#'         with the value being the element extracted by the corresponding
#'         regular expression.
#'
#' @examples
#' \dontrun{
#' lex("hello there 123.45", regexes=c(number=re$number, word="(\\w+)", whitespace="(\\s+)"))
#' }
#'
#' @import stringi
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
lex <- function(text, regexes, verbose=FALSE) {

  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  # disallow multiple capture groups in a single pattern.
  # i.e. regexes = c("(a|b)", "(c)|(d)")
  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  captured_groups <- stringi::stri_match_all(regexes, regex = "(?<!\\\\)\\([^?]")

  n_captured_groups <- vapply(captured_groups, FUN = function(x) {
    if (anyNA(x)) {
      0L
    } else {
      nrow(x)
    }
  }, integer(1))
  if (any(n_captured_groups > 1)) {
    stop("Regexes can define at most only a single capture group. Patterns which need fixing",
         deparse(regexes[n_captured_groups > 1]))
  }

  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  # Any regex that has 0 capture groups has its whole regex become the
  # capture group
  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  idx <- n_captured_groups == 0
  regexes[idx] <- paste0("(", regexes[idx], ")")

  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  # Insert a default pattern to match anything missed by the provided regexes
  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  regexes        <- c(regexes, .missing="(.)")
  regex_labels   <- names(regexes)

  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  # All regexes must be named
  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  stopifnot(!anyNA(regex_labels))
  stopifnot(!any(regex_labels == ''))

  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  # Combine all the patterns into a single regex
  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  regex <- paste(regexes, collapse='|')

  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  # Match all regex against the text
  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  token_matching  <- stringi::stri_match_all(text, regex = regex)[[1]]

  if (verbose) {
    colnames(token_matching) <- c("all", regex_labels)
    print(token_matching)
  }

  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  # Extract the actual token and the regex which matched the token
  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  regex_idx      <- apply(token_matching[, -1, drop=FALSE], 1, function(x) {  which(!is.na(x))})
  tokens         <- apply(token_matching[, -1, drop=FALSE], 1, function(x) {x[which(!is.na(x))]})

  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  # if 'regex_idx' is a list, then a location was matched by multiple regexes
  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  if (is.list(regex_idx)) {
    lens <- lengths(regex_idx)
    idx  <- which(lens > 1)
    stop("lex issues at the following locations within 'text': ", deparse(idx))
  }


  names(tokens)  <- regex_labels[regex_idx]

  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  # If any tokens were captured by the '.missing' regex, then show
  # a warning message
  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  if (verbose && any(names(tokens) == '.missing')) {
    not_captured <- sort(unique(tokens[names(tokens) == '.missing']))
    warning("The following characters were not captured: ", deparse(not_captured))
  }

  tokens
}



# nocov end