Hi Bob,
note that `scale()' returns a matrix! This should work:
Data1$xx <- scale(Data1$xx) sapply(Data1, data.class) #### Data1$xx <- c(scale(Data1$xx)) sapply(Data1, data.class)
I hope it helps.
Best, Dimitris
---- Dimitris Rizopoulos Ph.D. Student Biostatistical Centre School of Public Health Catholic University of Leuven
Address: Kapucijnenvoer 35, Leuven, Belgium Tel: +32/16/396887 Fax: +32/16/337015 Web: http://www.med.kuleuven.ac.be/biostat/ http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm
----- Original Message ----- From: "Anon." <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Wednesday, October 20, 2004 3:56 PM
Subject: [R] Odd behaviour with scale()
Moi!
A student here has been getting a bit irritated with some side effects of scale() (OS is Windows XP, the behaviour occurs in R 2.0.0, but not 1.7.1). The problem is that she scales a variable in a data frame, then does a regression, and tries to get some predictions for some new data. However, at this point she gets an error (see the example below). This seems to be because the scaled variable in the new data frame does not have the center and scale attributes, but the one in the old data frame does.
The work-around is to put the scaled variable intro a new data frame, which again won't have the attributes. But it seems odd to me that whether a scale()'d variable has attributes depends on where it's placed. I presume that this is because I'm not understanding something about the way R is working, rather than it being a bug. Would anyone care to enlighten me?
> Data1=data.frame(xx=1:10, yy=2.1:12)
> Data1$xx=scale(Data1$xx)
>
> reg1=lm(yy~xx, data=Data1)
> New=data.frame(xx=2:4)
> b=predict(reg1, New, se.fit=T)
Error: variable 'xx' was fitted with nmatrix.1 but numeric was supplied
>
> New=data.frame(xx=scale(2:4, center=5.5, scale=3.02))
> b=predict(reg1, New, se.fit=T)
Error: variable 'xx' was fitted with nmatrix.1 but numeric was supplied
>
Bob
-- Bob O'Hara Department of Mathematics and Statistics P.O. Box 68 (Gustaf Hällströmin katu 2b) FIN-00014 University of Helsinki Finland
Telephone: +358-9-191 51479 Mobile: +358 50 599 0540 Fax: +358-9-191 51400 WWW: http://www.RNI.Helsinki.FI/~boh/ Journal of Negative Results - EEB: www.jnr-eeb.org
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