formulr
In formulr: Miscelaneous tools to handle formulas.

formulr

This is a helper package used in rollply to handle formulas of the form a ~ b + c | d.

It converts this kind of formulas into a formulr object (actually a list) with three components, x,y and g (for groups) :

library(formulr)
form <- as.formulr(a ~ b + c | d)
str(form)

This object can then be eval'ed given some data and optionally an enclosing environment:

.dat <- data.frame(a=rnorm(10), 
                   b=runif(10), 
                   c=rpois(10,10), 
                   d=rbeta(10, 1, .5))
result <- eval.formulr(as.formulr(a ~ b + c | d), envir=.dat)
str(result)

This object can be then converted back to useful data structures:

df <- as.data.frame(result)
str(df)

df <- as.data.frame(result, collapse=TRUE)
round(df,digits=2)

Warning

formulr is still under heavy development and is mainly an externalisation of some tools needed by rollply rather than a full-blown package. It might turn into something more official one day though.

Use at your own risk.