dead-code/geom-quiver.R

In jmzobitz/MAT369Code: Simulating Differential Equations with Data

#' Quiver plots for ggplot2
#'
#' @description
#' Displays the direction and length of vectors on a graph.
#'
#' @inheritParams ggplot2::layer
#' @param center If \code{FALSE} (the default), the vector lines will start at the specified x and y. If \code{TRUE}, the arrows will be centered about x and y.
#' @param rescale If \code{FALSE} (the default), the vectors will not be rescaled. If \code{TRUE}, the vectors given by (u, v) will be rescaled using the \code{scale} function.
#' @param vecsize By default (NULL), vectors sizing is automatically determined. If a grid can be identified, they will be scaled to the grid, if not, the vectors will not be scaled. By specifying a numeric input here, the length of all arrows can be adjusted. Setting vecsize to zero will prevent scaling the arrows.
#'
#' @examples
#' # Quiver plots of mathematical functions
#' expand.grid(x=seq(0,pi,pi/12), y=seq(0,pi,pi/12)) %>%
#'   ggplot(aes(x=x,y=y,u=cos(x),v=sin(y))) +
#'   geom_quiver()
#'
#' # Removing automatic scaling
#' ggplot(seals, aes(x=long, y=lat, u=delta_long, v=delta_lat)) +
#'   geom_quiver(vecsize=NULL) +
#'   borders("state")
#'
#' \dontrun{
#' # Centering arrows is useful for plotting on maps.
#' library(dplyr)
#' library(ggmap)
#' wind_data <- wind %>% filter(between(lon, -96, -93) & between(lat, 28.7, 30))
#' qmplot(lon, lat, data=wind_data, extent="panel", geom = "blank", zoom=8, maptype = "toner-lite") +
#'   geom_quiver(aes(u=delta_lon, v=delta_lat, colour = spd), center=TRUE)
#' }
#'
#' @importFrom ggplot2 layer
#'
#' @export
geom_quiver <- function(mapping = NULL, data = NULL,
                        stat = "quiver", position = "identity",
                        center = FALSE,
                        rescale = FALSE,
                        vecsize = NULL,
                        na.rm = FALSE,
                        show.legend = NA,
                        inherit.aes = TRUE,
                        ...) {
  ggplot2::layer(
    data = data,
    mapping = mapping,
    stat = stat,
    geom = GeomQuiver,
    position = position,
    show.legend = show.legend,
    inherit.aes = inherit.aes,
    params = list(
      na.rm = na.rm,
      center = center,
      rescale = rescale,
      vecsize = vecsize,
      ...
    )
  )
}

#' @rdname geom_quiver
#'
#' @export
GeomQuiver <- ggproto(
  "GeomQuiver", ggplot2::GeomSegment,
  draw_panel = function(data, panel_params, coord, arrow = NULL, lineend = "butt", na.rm = FALSE) {
    trans <- CoordCartesian$transform(data, panel_params) %>%
      mutate(arrowsize = sqrt((x - xend) ^ 2 + (y - yend) ^ 2) * 0.5)
    grid::segmentsGrob(
      trans$x, trans$y, trans$xend, trans$yend,
      default.units = "native",
      gp = grid::gpar(
        col = alpha(trans$colour, trans$alpha),
        lwd = trans$size * .pt,
        lty = trans$linetype,
        lineend = lineend
      ),
      arrow = grid::arrow(length = unit(trans$arrowsize, "npc"))
    )
  }
)