expandDoubleVerts {lme4} R Documentation

## Expand terms with '||' notation into separate '|' terms

### Description

From the right hand side of a formula for a mixed-effects model, expand terms with the double vertical bar operator into separate, independent random effect terms.

### Usage

  expandDoubleVerts(term)


### Arguments

 term a mixed-model formula

### Value

the modified term

### Note

Because || works at the level of formula parsing, it has no way of knowing whether a variable is a factor. It just takes the terms within a random-effects term and literally splits them into the intercept and separate no-intercept terms, e.g. (1+x+y|f) would be split into (1|f) + (0+x|f) + (0+y|f). However, || will fail to break up factors into separate terms; the dummy function can be useful in this case, although it is not as convenient as ||.

formula, model.frame, model.matrix, dummy.

Other utilities: mkRespMod, mkReTrms, nlformula, nobars, subbars

### Examples

  m <- ~ x + (x || g)
expandDoubleVerts(m)
set.seed(101)
dd <- expand.grid(f=factor(letters[1:3]),g=factor(1:200),rep=1:3)
dd\$y <- simulate(~f + (1|g) + (0+dummy(f,"b")|g) + (0+dummy(f,"c")|g),
newdata=dd,
newparams=list(beta=rep(0,3),
theta=c(1,2,1),
sigma=1),
family=gaussian)[[1]]
m1 <- lmer(y~f+(f|g),data=dd)
VarCorr(m1)
m2 <- lmer(y~f+(1|g) + (0+dummy(f,"b")|g) + (0+dummy(f,"c")|g),
data=dd)
VarCorr(m2)


[Package lme4 version 1.1-32 Index]