search for: _predictor

Dear r-developers: I am struggling with some fundamental aspects of model.frame(). Conceptually, I think of a flow from data -> model.frame() -> model.matrix; the data contain _input variables_, while model.matrix contains _predictor variables_: data have been transformed, splines and polynomials have been expanded into their corresponding multi-dimensional bases, and factors have been expanded into appropriate sets of dummy variables depending on their contrasts. I originally thought of model.frame() as containing input vari...