Design Matrix for Random effects

Steve Walker <steve.walker at ...> writes:

Hi Robert,

In stable (i.e. cran) lme4, Zt can be obtained without fitting the model 
using this command:

lmer(Reaction ~ Days + (Days|Subject), data=sleepstudy, doFit = 
FALSE)$FL$trms[[1]]$Zt

In development (i.e. github) lme4, you can use this command:

lFormula(Reaction ~ Days + (Days|Subject), data=sleepstudy)$reTrms$Zt

or these two:

dv <- lmer(Reaction ~ Days + (Days|Subject), data=sleepstudy, 
devFunOnly 
= TRUE)
environment(dv)$pp$Zt

Cheers,
Steve

It can be done even one step more directly:

mkReTrms(list(quote(Days|Subject)),sleepstudy)$Zt

the slightly convoluted form of the first argument is because
mkReTrms (see ?mkReTrms) wants a list of the random-effects
bits extracted from the formula, so it needs to be a list
of 'language' objects.  Alternatively:

mkReTrms(findbars(~(Days|Subject)),sleepstudy)$Zt

 I have a minor preference for these because they depend
a little less on the detailed form in which things are
stored in the package.

  Ben Bolker