12.19 包络图

ggpubr 包提供了 stat_chull() 图层

library(ggpubr)
ggscatter(mpg, x = "displ", y = "hwy", color = "drv")+
 stat_chull(aes(color = drv, fill = drv), alpha = 0.1, geom = "polygon")

图 12.59: 包络图

其背后的原理如下

stat_chull

## function (mapping = NULL, data = NULL, geom = "path", position = "identity", 
##     na.rm = FALSE, show.legend = NA, inherit.aes = TRUE, ...) 
## {
##     layer(stat = StatChull, data = data, mapping = mapping, geom = geom, 
##         position = position, show.legend = show.legend, inherit.aes = inherit.aes, 
##         params = list(na.rm = na.rm, ...))
## }
## <bytecode: 0x563de265dba0>
## <environment: namespace:ggpubr>

StatChull <- ggproto("StatChull", Stat,
  compute_group = function(data, scales) {
    data[chull(data$x, data$y), , drop = FALSE]
  },
  required_aes = c("x", "y")
)

stat_chull <- function(mapping = NULL, data = NULL, geom = "polygon",
                       position = "identity", na.rm = FALSE, show.legend = NA,
                       inherit.aes = TRUE, ...) {
  layer(
    stat = StatChull, data = data, mapping = mapping, geom = geom,
    position = position, show.legend = show.legend, inherit.aes = inherit.aes,
    params = list(na.rm = na.rm, ...)
  )
}

ggplot(mpg, aes(displ, hwy)) + 
  geom_point() + 
  stat_chull(fill = NA, colour = "black")

ggplot(mpg, aes(displ, hwy, colour = drv)) + 
  geom_point() + 
  stat_chull(fill = NA)