R/geom_overhang_seats.R

In leeper/ggparliament: Parliament Plots

#' Draw overhang seats in mixed-member proportional (MMP) electoral systems
#' @param expr Expr refers to the designated overhang seats.
#' @examples
#' germany <- data.frame(
#'   year = 2013,
#'   seats = c(64, 63, 311, 193),
#'   government = c(0, 0, 1, 1),
#'   colour = c("#BE3075", "#64A12D", "#000000", "#EB001F"),
#'   party = c(
#'     "The Left",
#'     "Alliance 90/The Greens",
#'     "Christian Democratic Union",
#'     "Social Democratic Party"
#'   )
#' )
#' german_data <- parliament_data(
#'   election_data = germany,
#'   parl_rows = 11,
#'   party_seats = germany$seats,
#'   type = "semicircle"
#' )
#' german_data$overhang_seats <- rep(
#'   c(1, 0, 1, 0, 1, 0, 1, 0),
#'   c(16, 295, 11, 182, 3, 61, 3, 60)
#' )
#' ggplot2::ggplot(german_data, ggplot2::aes(x, y, colour = party)) +
#'   geom_parliament_seats() +
#'   geom_overhang_seats(overhang_seats == 1) +
#'   theme_ggparliament() +
#'   ggplot2::scale_colour_manual(
#'     values = as.character(german_data$colour),
#'     limits = as.character(german_data$party)
#'   )
#' @usage
#' geom_overhang_seats(expr)
#' @author Zoe Meers
#' @export
#' @importFrom ggplot2 ggplot_add


geom_overhang_seats <- function(expr) {
  structure(list(expr = rlang::enquo(expr)), class = "hangingseats")
}

#' @export
ggplot_add.hangingseats <- function(object, plot, object_name) {
  new_data <- dplyr::filter(plot$data, !!object$expr)
  new_layer <- ggplot2::geom_point(
    data = new_data,
    mapping = plot$mapping,
    fill = "white",
    show.legend = FALSE,
    shape = 21,
    size = 2,
    stroke = 0.5
  )
  plot$layers <- append(plot$layers, new_layer)
  plot
}