R/context.R

In smmurphy/convenience: Convenience Functions for R

#' Context
#' 
#' Find a substring and return with a buffer of n characters on either side.
#' @param term A regular expression to search for.
#' @param back The number of characters back to return.
#' @param forward The number of characters forward to return.
#' @param ignore.case Should case be ignored for the search. Default is TRUE.
#' @param highligh Should the returned expression be in CAPS? Default is TRUE.
#' @keywords search, grep, context, phrase
#' @export
#' @examples 
#' context()

context <-
  function (term = ".*",
            target = NULL,
            back = 20,
            forward = 20,
            ignore.case = TRUE,
            highlight = TRUE)
  {
    if (!is.null(target)) {
      matches <- target[grepl(term, target, ignore.case = ignore.case)]
      cPos <-
        gregexpr(pattern = term, matches, ignore.case = ignore.case)
      cPos <- unlist(lapply(cPos, `[[`, 1))
      str <- substr(
        matches,
        start = ifelse(cPos - back < 1,
                       1, cPos - back),
        stop = ifelse(
          cPos + nchar(term) + forward > nchar(matches),
          nchar(matches),
          cPos + nchar(term) + forward
        )
      )
      if (highlight == TRUE) {
        str <- gsub(paste0("(", term, ")"),
                    "\\U\\1",
                    str,
                    perl = TRUE,
                    ignore.case = ignore.case)
      }
      str <- paste0("...", str, "...")
    }
    return(str)
  }