r - 如何在 R 中使用曲线()对图形进行着色

Question

我正在绘制标准正态分布。

curve(dnorm(x), from=-4, to=4, 
  main = "The Standard Normal Distibution", 
  ylab = "Probability Density",
  xlab = "X")

出于教学原因，我想将低于我选择的某个分位数的区域涂上阴影。我怎样才能做到这一点？

Answer 1

如果您想使用 curve和基图，然后你可以用 polygon 自己写一个小函数:

colorArea <- function(from, to, density, ..., col="blue", dens=NULL){
    y_seq <- seq(from, to, length.out=500)
    d <- c(0, density(y_seq, ...), 0)
    polygon(c(from, y_seq, to), d, col=col, density=dens)
}

一个小例子如下:

curve(dnorm(x), from=-4, to=4, 
  main = "The Standard Normal Distibution", 
  ylab = "Probability Density",
  xlab = "X")

colorArea(from=-4, to=qnorm(0.025), dnorm)
colorArea(from=qnorm(0.975), to=4, dnorm, mean=0, sd=1, col=2, dens=20)