将ggplot ellips限制为现实/可能的值

Question

在使用ggplot绘制椭圆时,是否可以将椭圆约束为实际可能的值？

例如,以下可重现的代码和数据绘制了两种物种的Ele vs. Var.Var是一个正变量,不能为负数.尽管如此,负值仍包含在结果椭圆中.是否可以在x轴上将椭圆限制为0(使用ggplot)？

更具体地说,我想象的是一个扁平边缘,椭圆体在x轴上截断为0.

library(ggplot2)
set.seed(123)
df <- data.frame(Species = rep(c("BHS", "MTG"), each = 100),
                 Ele = c(sample(1500:3000, 100), sample(2500:3500, 100)),
                 Var = abs(rnorm(200)))

ggplot(df, aes(Var, Ele, color = Species)) +
  geom_point() +
  stat_ellipse(aes(fill = Species), geom="polygon",level=0.95,alpha=0.2) 

Answer 1

您可以编辑默认属性以将点剪辑为特定值.在这里,我们将基本属性更改为将小于0的x值修剪为0

StatClipEllipse <- ggproto("StatClipEllipse", Stat,
    required_aes = c("x", "y"),
    compute_group = function(data, scales, type = "t", level = 0.95,
       segments = 51, na.rm = FALSE) {
           xx <- ggplot2:::calculate_ellipse(data = data, vars = c("x", "y"), type = type,
               level = level, segments = segments)
           xx %>% mutate(x=pmax(x, 0))
      }
)

然后我们必须将它包装在一个ggplot stat中,stat_ellipe除了它使用我们的自定义Stat对象之外

stat_clip_ellipse <- function(mapping = NULL, data = NULL,
                         geom = "path", position = "identity",
                         ...,
                         type = "t",
                         level = 0.95,
                         segments = 51,
                         na.rm = FALSE,
                         show.legend = NA,
                         inherit.aes = TRUE) {
  layer(
    data = data,
    mapping = mapping,
    stat = StatClipEllipse,
    geom = geom,
    position = position,
    show.legend = show.legend,
    inherit.aes = inherit.aes,
    params = list(
      type = type,
      level = level,
      segments = segments,
      na.rm = na.rm,
      ...
    )
  )
}

然后你可以用它来制作你的情节

ggplot(df, aes(Var, Ele, color = Species)) +
  geom_point() +
  stat_clip_ellipse(aes(fill = Species), geom="polygon",level=0.95,alpha=0.2) 

这受到stat_ellipse源代码的启发.