R/web.R

In pbs-assess/ggspider: Make a Spider or Radar Plot with ggplot2

#' Title
#'
#' @param mydf A data frame. The first column holds the names for the 'web' data.
#' The remaining columns are the names of the 'spokes'.
#'
#' @return A data.frame in 'long' format with columns 'group', 'x', and 'y' where group
#'  holds the names of the 'web' data groups, with 'x' and 'y' representing points on each
#'  spoke, with each group having number of rows = number of spokes plus one (the first one
#'  repeats at the end so that plot lines will connect).
#'
#' @examples
#' \dontrun{
#' df <- data.frame(
#'   nm = c(
#'     "A", "B", "C",
#'     "A", "B", "C",
#'     "A", "B", "C",
#'     "A", "B", "C",
#'     "A", "B", "C"
#'   ),
#'   spk = c(
#'     "P1", "P1", "P1",
#'     "P2", "P2", "P2",
#'     "P3", "P3", "P3",
#'     "P4", "P4", "P4",
#'     "P5", "P5", "P5"
#'   ),
#'   value = c(
#'     .1, .2, .3,
#'     .4, .5, .6,
#'     .7, .8, .9,
#'     .10, .11, .12,
#'     .13, .14, .15
#'   )
#' )
#' ds <- tidyr::spread(df, key = "spk", value = "value")
#' web <- calc_web(ds)
#' }
calc_web <- function(mydf) {
  if (missing(mydf)) {
    stop("Argument 'mydf' is required",
      call. = FALSE
    )
  }
  if (!any("data.frame" %in% class(mydf)) || length(mydf) < 2 || nrow(mydf) < 1) {
    stop("Argument 'mydf' must be a data frame with at least one row and two columns")
  }
  df <- cbind(mydf[, -1], mydf[, 2])
  myvec <- c(t(df))
  angles <- seq(from = 0, to = 2 * pi, by = (2 * pi) / (ncol(df) - 1))
  xx <- myvec * sin(rep(c(angles[-ncol(df)], angles[1]), nrow(df)))
  yy <- myvec * cos(rep(c(angles[-ncol(df)], angles[1]), nrow(df)))
  data.frame(
    group = rep(as.character(mydf[, 1, drop = TRUE]),
      each = ncol(mydf)
    ),
    x = xx,
    y = yy
  )
}