在两点之间对内核密度图进行阴影处理. [英] Shading a kernel density plot between two points.

问题描述

我经常使用核密度图来说明分布.可以像这样在R中轻松轻松地创建它们:

I frequently use kernel density plots to illustrate distributions. These are easy and fast to create in R like so:

set.seed(1)
draws <- rnorm(100)^2
dens <- density(draws)
plot(dens)
#or in one line like this: plot(density(rnorm(100)^2))

哪个给我这个漂亮的小PDF:

Which gives me this nice little PDF:

我想将PDF下的区域阴影从第75个百分位数增加到第95个百分位数.使用quantile函数可以很容易地计算出点数:

I'd like to shade the area under the PDF from the 75th to 95th percentiles. It's easy to calculate the points using the quantile function:

q75 <- quantile(draws, .75)
q95 <- quantile(draws, .95)

但是如何为q75和q95之间的区域着色呢?

But how do I shade the the area between q75 and q95?

推荐答案

使用polygon()函数，请参阅其帮助页面，我相信这里也有类似的问题.

With the polygon() function, see its help page and I believe we had similar questions here too.

您需要找到分位数的索引才能获得实际的(x,y)对.

You need to find the index of the quantile values to get the actual (x,y) pairs.

在这里:

x1 <- min(which(dens$x >= q75))  
x2 <- max(which(dens$x <  q95))
with(dens, polygon(x=c(x[c(x1,x1:x2,x2)]), y= c(0, y[x1:x2], 0), col="gray"))

输出(由JDL添加)

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