[R] Plot and lm

[William Dunlap]

I think the problem is that plot's log axes are to the base 10
so the lm() call needs to use log10, not log.  E.g.,

   x<-101:200
   y<-sqrt(x)+1+runif(100)
   plot(x,y,log="xy")
   abline(col="red", lm(log(y)~log(x))) # nothing plotted
   abline(col="blue", lm(log10(y)~log10(x))) # passes through points

Expand the y axis a bit and you can see where the base-e line went:

   plot(x,y,log="xy", ylim=c(1,100))
   abline(col="red", lm(log(y)~log(x))) # plotted well above the points
   abline(col="blue", lm(log10(y)~log10(x))) # passes through points

Bill Dunlap
TIBCO Software Inc - Spotfire Division
wdunlap tibco.com  

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of stephen sefick
> Sent: Thursday, June 04, 2009 10:04 AM
> To: Par Leijonhufvud
> Cc: R-help
> Subject: Re: [R] Plot and lm
> 
> Could you provide a reproducible example even with fake data would be
> fine or dput() yours.
> 
> On Thu, Jun 4, 2009 at 10:11 AM, Par Leijonhufvud
> <par at hunter-gatherer.org> wrote:
> > I want to make a log-log plot with a regression line, but I 
> can't figure
> > out what I'm doing wrong. What I'm trying is:
> >
> > plot(mass,area, log="xy", pch=as.numeric(food))
> > abline(lm(mass~area))
> >
> > or
> >
> > plot(mass,area, log="xy", pch=as.numeric(food))
> > islands$logmass <- log(mass)
> > islands$logarea <- log(area)
> > attach(islands)
> > abline(lm(logmass~logarea))
> >
> >
> > But that does not show a line. Where am I going wrong?
> >
> > data:
> > island, area,species,food,mass
> > Ibiza , 577 ,  Anser n. sp., herb,  2.0
> > Ibiza , 577 ,    Haliaeetus albicilla, carn, 4.8
> > Mauritius , 1874 ,  Raphus cucullatus, herb,  19
> > Mauritius , 1874 ,  Circus alphonsi, carn, 0.63
> > Mallorca , 3667 , Myotragus balearicus, herb,  40
> > Mallorca , 3667 , Aquila chrysaetos, carn, 4.2
> > Kreta , 8259 , Elephas creutzburgi, herb,  3200
> > .......
> >
> > /Par
> >
> > --
> > Par Leijonhufvud                               
> par at hunter-gatherer.org
> > I don't believe in reincarnation.  I used to,
> > but that was in another life.
> >
> > ______________________________________________
> > R-help at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
> 
> 
> 
> -- 
> Stephen Sefick
> 
> Let's not spend our time and resources thinking about things that are
> so little or so large that all they really do for us is puff us up and
> make us feel like gods.  We are mammals, and have not exhausted the
> annoying little problems of being mammals.
> 
> 								
> -K. Mullis
> 
> ______________________________________________
> R-help at r-project.org mailing list
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> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>