Setup fixed effects part for longitudinal marker k (internal function) input:
setup_FE_model(formula, dataset, timeVar, k, dataOnly)
colnames(FE) names of the fixed effects (interactions are separated by ".X." instead of ":" to facilitate their manipulation)
FE values of the fixed effects
with lme4 format (fixed effects and random effects in the same object)
that contains the outcome
name of time variable
identifies the longitudinal marker among 1:K markers
boolean for internal use, indicates if only preparing data (i.e., not fitting the model) output: