# example of creating a function

sumdice <- function(n) {
	k <- sample(1:6,size=n,replace=TRUE)
	return(sum(k))}

n <- 2

repitions <- 100
outcomes <- rep(0,repitions)

# example of a for loop
for (i in 1:repitions){
	outcomes[i] <- sumdice(n)
	}

hist(outcomes)

# Data frame is a list of variables of the same length, but not necessarily the same type
library(DAAG)
data(ais)
help(ais)

is.data.frame(ais)
plot(ais)
head(ais)
names(ais)

attach(ais)
library(lattice)
xyplot(bmi~ssf|sport,groups=sex,pch=16,col=c(2,3),data=ais,xlab="Skin-fold",ylab="Body mass")
legend(x="topleft",legend=c("Females","Males"),pch=16,col=c(2,3))

x <- ais[,"bmi"]
y <- ais[,"pcBfat"]
plot(x,y,type="n",xlab="Body mass index",ylab="Percent body fat")

sport.name <- levels(sport)
n <- length(sport.name)
for (j in 1:n) {
	I <- sport==sport.name[j]
	x <- ais[I,"bmi"]
	y <- ais[I,"pcBfat"]
	star <- matrix(unlist(ais[I,1:5]),ncol=5)
	symbols(x,y,stars=star,add=TRUE,fg=j)
}
legend(x="topleft",legend=sport.name,pch=16,col=1:n)

x <- ais[,"bmi"]
y <- ais[,"pcBfat"]
plot(x,y,type="n",xlab="Body mass index",ylab="Percent body fat")

genders <- levels(sex)
n <- length(genders)
for (j in 1:n) {
	I <- sex==genders[j]
	x <- ais[I,"bmi"]
	y <- ais[I,"pcBfat"]
	star <- matrix(unlist(ais[I,1:5]),ncol=5)
	symbols(x,y,stars=star,add=TRUE,fg=j)
}
legend(x="topleft",legend=genders,pch=16,col=1:n)