Omit terms separated by vertical bars in a formula
nobars.RdRemove the random-effects terms from a mixed-effects formula, thereby producing the fixed-effects formula.
Note
This function is called recursively on individual terms
in the model, which is why the argument is called
term and not a name like form, indicating a
formula.
See also
formula, model.frame,
model.matrix.
Other utilities: findbars,
mkRespMod, mkReTrms,
nlformula, subbars