[R] How to use a function inside a regression formula

[Duncan Murdoch]

On 30/09/2011 2:07 PM, Jim Cheng wrote:
> Hi,
>
> How do I use a function inside a regression formula? When I tried to use
> min() function inside a regression formula,  I ran into errors.   Here are
> the commands to reproduce the error:
>
>
> mydata<- read.csv(url("http://www.ats.ucla.edu/stat/r/dae/binary.csv"))
>
> attach(mydata)
>
> names(mydata)
>
> mylm2 = lm(admit~gre+I(max(gpa,rank)))
>
> *Error in model.frame.default(formula = admit ~ gre + I(max(gpa, rank)),  :
>    variable lengths differ (found for 'I(min(gpa, rank))')*

min(gpa, rank) will be a length 1 vector.  You want pmin(gpa, rank).  (I 
haven't tried it in the regression, but it should work.)

Duncan Murdoch
> *
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> Regards,
>
> David
>
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