R help - May 2010 - what the problem could be if i am suddenly unable to add abline to the scatter plot?

I am doing very regular stuff like the following:


attach(wtana)

fm<- lm(Body.Wt.on.SD1~Heart.Wt, data=wtana)
#fm<- lm(wtana$Body.Wt.on.SD1~wtana$Heart.Wt)
lrf<- loess(Body.Wt.on.SD1~Heart.Wt, wtana)
#lrf<- loess(wtana$Body.Wt.on.SD1~wtana$Heart.Wt)

plot(Body.Wt.on.SD1,Heart.Wt)
#plot(wtana$Body.Wt.on.SD1,wtana$Heart.Wt)
#lines(spline(Heart.Wt,fitted(lrf)), col=2)
abline(fm, col=4)

however, the abline just refuse to to show up in the scatter cloud. 
Does anyone has clue?
thanks


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On May 12, 2010, at 11:57 AM, xin wei wrote:
>
> I am doing very regular stuff like the following:
>
>
> attach(wtana)
>
> fm<- lm(Body.Wt.on.SD1~Heart.Wt, data=wtana)
> #fm<- lm(wtana$Body.Wt.on.SD1~wtana$Heart.Wt)
> lrf<- loess(Body.Wt.on.SD1~Heart.Wt, wtana)
> #lrf<- loess(wtana$Body.Wt.on.SD1~wtana$Heart.Wt)
>
> plot(Body.Wt.on.SD1,Heart.Wt)
> #plot(wtana$Body.Wt.on.SD1,wtana$Heart.Wt)
> #lines(spline(Heart.Wt,fitted(lrf)), col=2)
> abline(fm, col=4)
>
> however, the abline just refuse to to show up in the scatter cloud.
> Does anyone has clue?
I don't know that abline has a method for lm objects.

 > methods(abline)
no methods were found
Warning message:
In methods(abline) : function 'abline' appears not to be generic

  Have you tried using coef(lm) as your argument to abline? (Untested  
in the absence of a cut-and-pastable example.)
> thanks
--

David Winsemius, MD
West Hartford, CT

Xin, you plot the scatterplot wrongly.

Note that the lm (your OLS regression) has a wiggle, whereas you plot
command has a comma. The plot command also should have a wiggle so that you
plot y against x and not x against y. See example below:

x=rnorm(100);e=rnorm(100)

y=2*x+e
reg=lm(y~x)

par(mfcol=c(1,2))

#This is wrong)
plot(y,x)
abline(reg)

#This is right
plot(y~x)
abline(reg)
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Just a quick addendum: You actually plot the line. If it is not in the graph
then just because it is outside the limits of the plotting region. But since
it's the right line on the wrong plot, it does not matter anyway. You need
to get the plot right first, which you do in the way I described above.

Daniel
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