Works for all the fitters. In the multi-trait case the coefficients come named
"level|trait"; use trait= to slice out one trait.
Arguments
- fit
result of model(), model_mt() or snp_blup()
- group
covariance group; by default the group of the direct genetic term: the first pedigree or genomic term that is not
maternal(), else the firstmaternal()term, else the first group; the same default inebv(),solutions(),accuracy(),h2()andh2_curve()- trait
multi-trait only: which trait to slice out; all of them if omitted