R/plot_cores.R

In redist: Simulation Methods for Legislative Redistricting

#' Plot Cores
#'
#' @param shp A SpatialPolygonsDataFrame or sf object. Required.
#' @param plan A numeric vector with one entry for each precinct in shp.
#' Used to color the districts. Required.
#' @param core Required. integer vector produced by \code{redist.identify.cores()}.
#' @param lwd Line width. Defaults to 2.
#'
#' @importFrom dplyr if_else
#'
#' @return ggplot
#' @export
#' @concept plot
redist.plot.cores <- function(shp, plan = NULL, core = NULL, lwd = 2) {
    plan <- eval_tidy(enquo(plan), shp)
    if (is.null(plan)) {
        if (inherits(shp, "redist_map")) {
            plan <- get_existing(shp)
        } else {
            cli_abort("{.arg plan} is required if {.arg shp} is not a {.cls redist_map}.")
        }
    }

    core <- eval_tidy(enquo(core), shp)
    if (missing(core)) {
        cli_abort("{.arg core} is required.")
    }

    shp$plan <- plan
    shp$core <- core

    shp_un <- shp %>%
        group_by(plan) %>%
        summarize(geometry = st_union(geometry),
            .groups = "drop") %>%
        suppressMessages()

    shp_cores <- shp %>%
        group_by(plan, core) %>%
        summarize(ct = n(),
            geometry = st_union(geometry),
            .groups = "drop") %>%
        mutate(ct = if_else(.data$ct == 1, NA_integer_, .data$ct)) %>%
        suppressMessages()

    shp_cores %>%
        ggplot() +
        geom_sf(aes(fill = .data$ct)) +
        ggplot2::scale_fill_distiller(direction = 1, na.value = "white") +
        geom_sf(fill = NA, data = shp_un, color = "black", lwd = lwd) +
        labs(fill = "Number of Units in Core") +
        theme_void() +
        theme(legend.position = "bottom")
}