Translates the optional group_contrasts specification into a list of contrast
records. Each record holds a weight vector over the group levels (weights, in
factor-level order, summing to zero), the output parameter name, an optional
user label, and the level_1 / level_2 group labels for simple pairwise
contrasts (NA for general weight-vector contrasts).
ancova_resolve_contrasts(group_contrasts, orig_levels, labels)A list of contrast records (see description).
Either NULL or a fully named list of length-2 character
vectors and/or numeric weight vectors. See set_vars().
Character vector of the group factor levels (in order).
Character vector of ref/alt/... labels from ancova_group_labels().
When group_contrasts is NULL the default is each non-reference level versus the
reference level, using the backwards-compatible trt / trt_alt2 / ... naming.
Otherwise the list must be fully named; each element is either a length-2 character
vector c(minuend, subtrahend) (a pairwise contrast) or a numeric weight vector over
the group levels, and the list name is used as the parameter name.