r-confusions.R

> # Setup data
> names <- c("Field 1","Field 2","Field 3")
> area  <- c(1.3,1.4,1.1)
> soil  <- factor(c("wet","dry","wet"))
> worms <- data.frame(names,area,soil)
> worms
    names area soil
1 Field 1  1.3  wet
2 Field 2  1.4  dry
3 Field 3  1.1  wet

> # Group area vector by soil type vector
> # and find the mean of each group
> by(worms$area,worms$soil,mean)
soil: dry
[1] 1.4
soil: wet
[1] 1.2