I'm inspecting tests/usersplits.R in rpart, trying to get my head around how to pass data to the split function. I'm trying to instantiate a number of goodness measures which compare treatment vs control within splits. A simple example is difference-in-difference estimate of a candidate split, (Y_t - Y_c)_L - (Y_t - Y_c)_R (difference between treatment and control for the left minus difference between treatment and control for the right) I need to know whether each Y value is a treatment Y or a control. the documentation in usersplits.R says that Y is provided in sort order of X, so I'm not sure how to pass a vector indicating treatment vs control that will split Y appropriately. rpart.poisson takes a two column matrix as an input, and I've been trying to mimic that, but there's no documentation in rpart.poisson (i can't figure out where it creates the 'vector of goodness') I'd appreciate any advice, J. Cress -- View this message in context: http://r.789695.n4.nabble.com/rpart-usersplits-tp4342156p4342156.html Sent from the R help mailing list archive at Nabble.com.