[R] Annotate a segmented linear regression plot
David Winsemius
dwinsemius at comcast.net
Wed Oct 3 01:57:12 CEST 2012
On Oct 2, 2012, at 3:38 PM, Ben Harrison wrote:
> On 28 September 2012 16:38, David Winsemius <dwinsemius at comcast.net> wrote:
>>
>> ?text # should be fairly clear.
>
> Thank you. I was stupid to ask such a trivial question along with a
> not-so-trivial one. The second part of the question was probably more
> important: is there a way to obtain the location of segments produced
> by the segmented package, so that I can annotate them easily?
I guess it depends on what you mean by "the location of segments". It's easy enough to retrun the x-values for the knots:
o$psi[ , "Est."]
I do not see a `predicted.segmented` function, so might need to construct separate lm.predict estimates for values between the pairs of x-values if you meant you wanted the y-values for the knots.
--
David.
>
> I have since asked this question of Vito, the package's author. Here
> is his response:
>
> #####
> dear Ben,
> here a possible solution,
>
> o is the segmented fit
>
> r<-o$rangeZ[,1]
> est.psi<-o$psi[,2]
> v<-sort(c(r, est.psi))
> xCoord<-rowMeans(cbind(v[-length(v)], v[-1]))
>
> Z<-o$model[,o$nameUV$Z]
>
> id<-sapply(xCoord, function(x)which.min(abs(x-Z)))
> yCoord<-broken.line(o)[id]
>
> plot(o, col=2:4, res=T)
> text(xCoord, yCoord, labels=formatC(slope(o)[[1]][,1], digits=2),
> pos=4, cex=1.3)
>
> Play with pos, cex and digits to modify the appearance of the labels.
>
> vito
> #####
>
>> Please learn to post in plain text.
>
> I hope this is better.
>
> Ben.
David Winsemius, MD
Alameda, CA, USA
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