[R] How to shade part of a density plot

[Uwe Ligges]

Stuart Luppescu wrote:
> 
> I'm trying to shade part of a density plot. The code I'm trying (using
> the Old Faithful data as an example) is something like this:
> 
> # The Old Faithful geyser data
> data(faithful)
> d <- density(faithful$eruptions, bw = "sj")
> plot(d)
> polygon(d[d$x>4], col = "wheat")

Hmm. Have a look at
  str(d)
to see that d is a density object, which is a list of objects of
different lengths, so indexing as you did doesn't work ...

What about taking 
  index <- d$x > 4
and working with
  d$x[index] and d$y[index]
to generate the shading?

Uwe Ligges


> I expected that the part of the curve to the right of 4 on the x axis
> should be shaded, but nothing gets shaded at all. In fact, when I just
> try to print d[d$x>4] I get many lines of
> $"NA"
> NULL
> I must be mistaken in my understanding of density objects. Could someone
> clear up my mistake? Thanks very much.
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