> On 11 Mar 2016, at 08:25 , David Winsemius <dwinsem...@comcast.net> wrote: >> ... >>> dfrm <- data.frame(y=rnorm(10), x1=rnorm(10) ,x2=as.factor(TRUE), >>> x3=rnorm(10)) >>> lm(y~x1+x2+x3, dfrm, na.action=na.exclude) >> Error in `contrasts<-`(`*tmp*`, value = contr.funs[1 + isOF[nn]]) : >> contrasts can be applied > > Yes, and the error appears to come from `model.matrix`: > >> model.matrix(y~x1+factor(x2)+x3, dfrm) > Error in `contrasts<-`(`*tmp*`, value = contr.funs[1 + isOF[nn]]) : > contrasts can be applied only to factors with 2 or more levels >
Actually not. The above is because you use an explicit factor(x2). The actual smoking gun is this line in lm() mf$drop.unused.levels <- TRUE which someone must have thought was a good idea at some point.... model.matrix itself is quite happy to leave factors alone and let subsequent code sort out any singularities, e.g. > model.matrix(y~x1+x2, data=df[1:2,]) (Intercept) x1 x2B 1 1 1 0 2 1 1 0 attr(,"assign") [1] 0 1 2 attr(,"contrasts") attr(,"contrasts")$x2 [1] "contr.treatment" >> model.matrix(y~x1+x2+x3, dfrm) > (Intercept) x1 x2TRUE x3 > 1 1 0.04887847 1 -0.4199628 > 2 1 -1.04786688 1 1.3947923 > 3 1 -0.34896007 1 -2.1873666 > 4 1 -0.08866061 1 0.1204129 > 5 1 -0.41111366 1 -1.6631057 > 6 1 -0.83449110 1 1.1631801 > 7 1 -0.67887823 1 0.3207544 > 8 1 -1.12206068 1 0.6012040 > 9 1 0.05116683 1 0.3598696 > 10 1 1.74413583 1 0.3608478 > attr(,"assign") > [1] 0 1 2 3 > attr(,"contrasts") > attr(,"contrasts")$x2 > [1] "contr.treatment" > > -- > > David Winsemius > Alameda, CA, USA > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. -- Peter Dalgaard, Professor, Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Office: A 4.23 Email: pd....@cbs.dk Priv: pda...@gmail.com ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
