# [R] R] highlight an area below a line

Peter Dalgaard p.dalgaard at biostat.ku.dk
Mon Mar 20 21:34:08 CET 2006

```Georg Otto <georg.otto at tuebingen.mpg.de> writes:

> Thanks a lot for your help!
>
> Now I have a related problem, that I still can not solve:
>
> I plot a t distribution using:
>
> curve(dt(x, df = 20), xlim=c(-5,5))
>
> The upper 5% of that distribution using:
>
> qt(0.05, df=20, lower.tail=FALSE)
>
> How can define the polygon to highlight the area representing the
> upper 5% of values?

curve(dt(x, df = 20), xlim=c(-5,5))
x0 <- qt(0.05, df=20, lower.tail=FALSE)
xmax <- 5
x <- seq(x0, xmax, length=100) # or whatever it takes
polygon(c(x0, x, xmax),c(0, dt(x, df = 20), 0), col="red")

> Thanks a lot!
>
> Georg
>
> "Ken Knoblauch" <knoblauch at lyon.inserm.fr> writes:
>
> > How about,
> >
> > d<-density(rnorm(10000))
> > plot(d)
> > wvs <- which(d\$x > 1 & d\$x < 2)
> > polygon(d\$x[c( wvs[1], wvs, wvs[length(wvs)] ) ], c(0, d\$y[wvs], 0), col =
> > "bisque")
> >
> > Georg Otto a écrit:
> > Hi,
> >
> > if I plot a normal distribution like this:
> >
> > d<-density(rnorm(10000))
> > plot(d)
> >
> > how can I highlight the area below the graph in a certain interval,
> > say x=1,2?  I understand that I should use polygon, but I have not
> > found the right way to give the result that I want.
> >
> > .
>
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--
O__  ---- Peter Dalgaard             Øster Farimagsgade 5, Entr.B
c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
(*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)                  FAX: (+45) 35327907

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