[R] Problem using predict() to draw lines() if predictor variable is logged on the fly

[Adams, Jean]

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Jean

On Thu, Oct 2, 2014 at 11:12 AM, <mtb954 at gmail.com> wrote:

> Hello,
>
> I am plotting glms with logged predictors. I would like to define the
> logged variables "on the fly" rather than hard coding them into my
> dataframe.
>
> This code (with hard-coded logged variables) works just fine:
>
> xx<-seq(-2,.5,by=0.1); lines(xx,predict(power,list(LogArKm00=xx),type=
> "response"),col="black",lwd=2,lty=1) #LogArKm00 is a variable in my
> dataframe
>
> but my attempt to define them "on the fly" doesn't work (see error below):
>
> plot(log(WbAb,10)~log(ArKm00,10),data=dat) #power model
>
> xx<-seq(-2,.5,by=0.1); lines(xx,predict(power,list(log(ArKm00,10)=xx),type=
> "response"),col="black",lwd=2,lty=1) #trying to log the variable "on the
> fly"
>
>
> Error: unexpected '=' in " lines(xx,predict(power,list(log(ArKm00,10)="
>
> I would really appreciate any help sorting this out!
>
> Many thanks
>
> Mark
>
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