[R] Calculating mean together with split

[hadley wickham]

> # Then try one of these:
>
> cast(dfm, year ~ sim)
> cast(dfm, year + sim ~ . )
> cast(dfm, year ~ sim, margins=TRUE)

Oops that should be:

dfm <- rename(df, c(DensPlants = "value"))

cast(dfm, year ~ sim, mean)
cast(dfm, year + sim ~ . , mean)
cast(dfm, year ~ sim, mean, margins=TRUE)

(Thanks for pointing that out Gabor!)

Hadley