r - 如何在我用类型 ='s' 绘制的线下填充

Question

我想填充我使用 plot(X, type='s') 绘制的阶梯函数线下的区域我试过 polygon没有成功。

set.seed(1);y = abs(rnorm(10))
plot(y,ylim=c(0,max(y)), type="p",pch=24)
lines(y, type='s')
abline(h=0)

假设我想在曲线下方和上方绘制灰色 y=0

Answer 1

x <- seq_along(y)
y2 <- rep(y, each=2)
y2 <- y2[-length(y2)]
x2 <- rep(x, each=2)[-1]
x3 <- c(min(x2), x2, max(x2))
y3 <- c(0, y2, 0)

# because polygon() is dumb and wants a pre-existing plot
plot(x, y, ylim=c(0, max(y)), type="n")

polygon(x3, y3, border=NA, col="grey")
lines(x2, y2)