[R] how to fill the area under the density line with semitransparent colors

[Mao Jianfeng]

Dear R-listers,

I have created a plot to display the density lines for the same
variable by different entities. Now, I want to fill the area under the
density lines with semitransparent colors.
Though I have checked that in web-searching and book-reading, I still
do not perform that.

Could anyone please give me any helps or advice? Thank you in advance.

The data and code I used listed below:

# dummy data
factor<-rep(c("Alice","Jone","Mike"),each=100)
factor<-factor(factor)
traits<-c(rnorm(100, mean=1, sd=1), rnorm(100, mean=3, sd=3),
rnorm(100, mean=6, sd=6))
myda<-data.frame(factor,traits)

# my plot
plot(c(min(myda$traits),max(myda$traits)),c(-0.03,0.5), xlab='State',
ylab='ylab')
lines(density(myda$traits[factor==c("Alice")]), lwd=2,col=2)
lines(density(myda$traits[factor==c("Jone")]), lwd=2,col=3)
lines(density(myda$traits[factor==c("Mike")]), lwd=2,col=4)
points(myda$traits[factor==c("Alice")], rep(-0.01,
length(myda$traits[factor==c("Alice")])), pch="|", col=2)
points(myda$traits[factor==c("Jone")], rep(-0.02,
length(myda$traits[factor==c("Jone")])), pch="|", col=3)
points(myda$traits[factor==c("Mike")], rep(-0.03,
length(myda$traits[factor==c("Mike")])), pch="|", col=4)

Regards,

Yours
Mao J-F