cristian at biometria.univr.it wrote:> Hi!
>
> How can I fill with colors a portion of a graph (e.g.: I want fill in red
the
> area within two confidence intervals)?
You can construct the coordinates of the polygon that fills this
region, then use 'polygon' to fill it. Here:
# first set up the plot - we want the density over the polygon,
# so make a blank plot of the right size:
x <- seq(-3,3,len=100)
plot(x,dnorm(x),type='n')
# a little function that draws a filled polygon between limits under
# dnorm(x) The polygon has to go from the axis, up, along the curve,
# then back down again.
fillDnorm <- function(low,high,col="red",n=100){
x <- seq(low,high,len=n)
y <- dnorm(x)
x <- c(x[1],x,x[length(x)])
y <- c(0,y,0)
polygon(x,y,col=col,border=NA)
}
# fill between -2 and -1
fillDnorm(-2,-1)
# now add the density
lines(x,dnorm(x))
Tweak as required.
Baz