Returns the model frame from a formula and data set. This routine is intended to only be called from within other Rdistance functions.
getDfuncModelFrame(formula, data)
a model frame containing the response and covariates resulting from evaluating formula in data.
A dfunc formula object. See dfuncEstim
.
The data frame from which variables in formula (potentially) come.
This routine is needed to get the scoping correct in dfuncEstim
.
In dfuncEstim
, we first merge the detection and site data frames, then
call this routine.