R/sort.r

In vegalite: Tools to Encode Visualizations with the 'Grammar of Graphics'-Like 'Vega-Lite' 'Spec'

#' Create a sort definition object
#'
#' You can sort by aggregated value of another “sort” field by creating a
#' sort field definition object. All three properties must be non-\code{NULL}.
#'
#' @param field the field name to aggregate over.
#' @param op a valid \href{http://vega.github.io/vega-lite/docs/sort.html#aggregate}{aggregation operator}.
#' @param order either \code{ascending} or \code{descending}
#' @encoding UTF-8
#' @export
#' @examples
#' vegalite() %>%
#'   add_data("https://vega.github.io/vega-editor/app/data/cars.json") %>%
#'   encode_x("Horsepower", type="quantitative", aggregate="mean") %>%
#'   encode_y("Origin", "ordinal", sort=sort_def("Horsepower", "mean")) %>%
#'   mark_bar()
sort_def <- function(field, op=NULL, order=c("ascending", "descending")) {
  if (is.null(field) | is.null(op) | is.null(order)) {
    message(paste0("One or more sort definition components is NULL. ",
                   "Reverting to 'ascending' basic sort", sep="", collapse=""))
    return("ascending")
  } else {
    return(list(field=field, op=op, order=order[1]))
  }
}