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#' Show edges as a density map
#'
#' This geom makes it possible to add a layer showing edge presence as a density
#' map. Each edge is converted to `n` points along the line and a jitter is
#' applied. Based on this dataset a two-dimensional kernel density estimation is
#' applied and plotted as a raster image. The density is mapped to the alpha
#' level, making it possible to map a variable to the fill.
#'
#' @inheritSection geom_edge_link Edge aesthetic name expansion
#'
#' @section Aesthetics:
#' `geom_edge_density` understand the following aesthetics. Bold aesthetics are
#' automatically set, but can be overwritten.
#'
#' **x**
#' **y**
#' **xend**
#' **yend**
#' edge_fill
#' filter
#'
#'
#' @section Computed variables:
#'
#' \describe{
#' \item{x, y}{The coordinates for each pixel in the raster}
#' \item{density}{The density associated with the pixel}
#' }
#'
#' @inheritParams geom_edge_link
#' @inheritParams ggplot2::geom_raster
#'
#' @param n The number of points to estimate in the x and y direction, i.e. the
#' resolution of the raster.
#'
#' @author Thomas Lin Pedersen
#'
#' @family geom_edge_*
#'
#' @examples
#' require(tidygraph)
#' gr <- create_notable('bull') %>%
#' activate(edges) %>%
#' mutate(class = sample(letters[1:3], n(), replace = TRUE))
#'
#' ggraph(gr, 'stress') +
#' geom_edge_density(aes(fill = class)) +
#' geom_edge_link() + geom_node_point()
#' @rdname geom_edge_density
#' @name geom_edge_density
#'
NULL
#' @rdname ggraph-extensions
#' @format NULL
#' @usage NULL
#' @importFrom ggforce StatLink
#' @importFrom MASS bandwidth.nrd kde2d
#' @export
StatEdgeDensity <- ggproto('StatEdgeDensity', Stat,
compute_group = function(data, scales, na.rm = FALSE, h = NULL,
n = 100, bins = NULL, binwidth = NULL) {
group <- data$group[1]
x_range <- diff(range(c(data$x, data$xend)))
y_range <- diff(range(c(data$y, data$yend)))
x_extend <- x_range / 10
y_extend <- y_range / 10
data <- StatLink$compute_panel(data, n = 50)
data <- PositionJitter$compute_layer(data, list(
width = x_extend,
height = y_extend
))
if (is.null(h)) {
h <- c(MASS::bandwidth.nrd(data$x), MASS::bandwidth.nrd(data$y))
}
dens <- MASS::kde2d(data$x, data$y,
h = h, n = n,
lims = c(
scales$x$dimension(),
scales$y$dimension()
) + c(
-x_extend,
x_extend,
-y_extend,
y_extend
)
)
df <- expand.grid(x = dens$x, y = dens$y)
df$z <- as.vector(dens$z)
df$group <- group
names(df) <- c('x', 'y', 'density', 'group')
df
},
setup_data = function(data, params) {
StatFilter$setup_data(data, params)
},
default_aes = aes(filter = TRUE),
required_aes = c('x', 'y', 'xend', 'yend')
)
#' @rdname ggraph-extensions
#' @format NULL
#' @usage NULL
#' @importFrom grid gTree gList grobName rasterGrob rectGrob gpar
GeomEdgeDensity <- ggproto('GeomEdgeDensity', GeomRaster,
draw_panel = function(self, data, panel_scales, coord, ...) {
groups <- split(data, factor(data$group))
max_density <- max(rowSums(inject(cbind(!!!lapply(groups, `[[`, i = 'density')))))
grobs <- lapply(groups, function(group) {
self$draw_group(group, panel_scales, coord,
max.alpha = max_density,
...
)
})
grobs <- gTree(children = inject(gList(!!!grobs)))
grobs$name <- grobName(grobs, 'geom_edge_density')
grobs
},
draw_group = function(self, data, panel_scales, coord, max.alpha) {
if (!inherits(coord, 'CoordCartesian')) {
cli::cli_abort('{.fn {snake_class(self)}} only works with {.fn coord_cartesian')
}
data <- coord$transform(data, panel_scales)
x_pos <- as.integer((data$x - min(data$x)) / resolution(
data$x,
FALSE
))
y_pos <- as.integer((data$y - min(data$y)) / resolution(
data$y,
FALSE
))
nrow <- max(y_pos) + 1
ncol <- max(x_pos) + 1
raster <- matrix(NA_character_, nrow = nrow, ncol = ncol)
raster[cbind(nrow - y_pos, x_pos + 1)] <- alpha(
data$edge_fill,
data$density / max.alpha
)
x_rng <- c(min(data$xmin, na.rm = TRUE), max(data$xmax, na.rm = TRUE))
y_rng <- c(min(data$ymin, na.rm = TRUE), max(data$ymax, na.rm = TRUE))
rasterGrob(raster,
x = mean(x_rng), y = mean(y_rng),
width = diff(x_rng), height = diff(y_rng),
default.units = 'native', interpolate = TRUE
)
},
draw_key = function(data, params, size) {
rectGrob(gp = gpar(
col = NA,
fill = alpha(data$edge_fill %||% data$fill %||% "darkgrey"),
lty = 0
))
},
required_aes = c('x', 'y'),
default_aes = aes(edge_fill = 'darkgrey')
)
#' @rdname geom_edge_density
#'
#' @importFrom ggforce StatLink
#' @export
geom_edge_density <- function(mapping = NULL, data = get_edges('short'),
position = 'identity', show.legend = NA,
n = 100, ...) {
mapping <- complete_edge_aes(mapping)
mapping <- aes_intersect(mapping, aes(x = x, y = y,
xend = xend, yend = yend))
layer(
data = data, mapping = mapping, stat = StatEdgeDensity,
geom = GeomEdgeDensity, position = position,
show.legend = show.legend, inherit.aes = FALSE,
params = expand_edge_aes(
list2(n = n, ...)
)
)
}
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