Message-ID: <20060104173424.B5A0419FE8@slim.kubism.ku.dk>
Date: 2006-01-04T17:34:24Z
From: Peter Dalgaard
Subject: update.formula gotcha (PR#8462)
(Reported by S?ren H?jsgaard)
Looks like update.formula is stripping of parentheses in cases where
they shouldn't be
> update.formula (Reaction ~ Days + (Days | Subject), . ~ . + I(Days^2))
Reaction ~ Days + Days | Subject + I(Days^2)
Notice that the right hand side is interpreted with the bar at the root
of the parse tree, as in
(Days + Days) | (Subject + I(Days^2)):
> f <- update.formula (Reaction ~ Days + (Days | Subject), . ~ . + I(Days^2))
> f[[3]]
Days + Days | Subject + I(Days^2)
> f[[3]][[1]]
`|`
This confuses lmer() rather badly:
library(lme4)
example(lmer)
update(fm1,formula = . ~ . + I(Days^2))
------>
Error in x[[2]] : object is not subsettable
Error in model.matrix(eval(substitute(~T, list(T = x[[2]]))), frm) :
unable to find the argument 'object' in selecting a method for function 'model.matrix'
--
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