[R] problem with model.matrix

[Balasubramanian Narasimhan]

Trevor's problem is reproducible on  R 1.8.1 (which is what he was using) on
both Linux RHEL 3.0 and Solaris and R 1.8.0 on Windows.


----- Original Message ----- 
From: "Trevor Hastie" <hastie at stanford.edu>
To: <r-help at stat.math.ethz.ch>
Sent: Thursday, June 24, 2004 3:12 PM
Subject: [R] problem with model.matrix


> This works:
>
>
> > model.matrix(~I(pos>3),data=data.frame(pos=c(1:5)))
>   (Intercept) I(pos > 3)TRUE
> 1           1              0
> 2           1              0
> 3           1              0
> 4           1              1
> 5           1              1
> attr(,"assign")
> [1] 0 1
> attr(,"contrasts")
> attr(,"contrasts")$"I(pos > 3)"
> [1] "contr.treatment"
>
>
> This does not:
>
> > model.matrix(~I(pos>3),data=data.frame(pos=c(1:2)))
> Error in "contrasts<-"(`*tmp*`, value = "contr.treatment") :
>  contrasts can be applied only to factors with 2 or more levels
>
>
> --------------------------------------------------------------------
>   Trevor Hastie                                  hastie at stanford.edu
>   Professor, Department of Statistics, Stanford University
>   Phone: (650) 725-2231 (Statistics)          Fax: (650) 725-8977
>   (650) 498-5233 (Biostatistics)   Fax: (650) 725-6951
>   URL: http://www-stat.stanford.edu/~hastie
>   address: room 104, Department of Statistics, Sequoia Hall
>            390 Serra Mall, Stanford University, CA 94305-4065
> --------------------------------------------------------------------
>
> [[alternative HTML version deleted]]
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