problem in predict.lm(type="terms", terms=someNames, interval="confidence", ...)

R's predict.lm() fails when trying to compute
term-wise confidence (or prediction) intervals
for a subset of the terms in a model:

dat <- data.frame(y=log(1:10), x=1:10,

fac=rep(LETTERS[11:13],c(3,3,4)))

fit <- lm(y~fac*x, data=dat)
# can compute intervals for all terms
pfit <- predict(fit, type="terms", interval="confidence",

newdata=dat[7:5,])

# error computing intervals for a subset of the terms
pfit2 <- predict(fit, type="terms", terms=c("x","fac"),

interval="confidence", newdata=dat[7:5,])Error in predictor + hwid :
non-conformable arrays

# pfit2 should be the same as pfit2Expected
pfit2Expected <- lapply(pfit2,

function(x)if(is.matrix(x)) structure(x[, c("x","fac")],
constant=attr(x, "constant")) else x)


Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com