[R] How to include an externally defined NULL value in lm

Matthieu Stigler stigler3 at etu.unige.ch
Mon Mar 3 23:07:09 CET 2008


Hello!

I would love to be able to include an external variable  to a lm call, I 
mean something:

if(TRUE)
    a<-freeny.x[,4]
else
    a<-NULL

lm(freeny.y~freeny.x[,-4] +a)

but it does not work with a<-NULL, whereas

lm(freeny.y~freeny.x[,-4] +NULL)

I don't understand why and did not find an answer in the manuals... do 
you see it? Any idea?

Thanks!!



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