R/reverse.lookup.R

In searchable: Tools for Custom Searches / Subsets / Slices of Named R Objects

#' Perform a reverse lookup on searchables 
#' 
#' This function causes the pattern search to be performed against an object's
#' values instead of its names
#' 
#' @param string pattern for which to match against an objects values
#' 
#' \code{reverse.lookup} sets and toggles the logical attribute with name 
#' \code{reverse.lookup}. Actual implementation of the reverse lookup is 
#' performed in the Extract methods. 
#' 
#' 
#' In order to perform a reverse lookup, values must be converted to character 
#' names.
#' 
#' @section reverse.lookup:
#' 
#' When performing a reverse lookup, values (not names) are searched. The 
#' corresponding names are returned.  NOTE: this is highly experimental and only
#' works for atomic vectors. It is uncertain how this might be applied to 
#' recursive structures like lists. 
#' 
#' @return 
#'   a string object with the \code{reversse.lookup} attribute set. 
#' 
#' @seealso 
#'   The \code{invert} function in the \code{hash} package \cr
#'   
#' @examples 
#'   reverse.lookup("string")
#'   
#' @note
#'   What happens if there are two reverse.lookups
#' @rdname reverse.lookup
#' @export 

reverse.lookup <- 
  function(string) {
    orig <- attr(string, 'reverse.lookup', exact=TRUE )
    if( is.null(orig) )
      structure( string, reverse.lookup = TRUE ) else 
      structure( string, reverse.lookup = ! orig ) 
  }   


# GET AND SET REVERSE LOOKUP
#
# @examples
#  .reverse.lookup("hello")
#  .reverse.lookup("hello"  %>% reverse.lookup )

.reverse.lookup <- function(object) 
  ! is.null( attr(object,'reverse.lookup') ) &&
  attr(object,'reverse.lookup')

`.reverse.lookup<-` <- function(object, value) { 
  attr(object,'reverse.lookup') <- value
  return(object)
}