[R] Rotated text on a regression line

From: Dr. Christoph Scherber <Christoph.Scherber_at_agr.uni-goettingen.de>
Date: Tue, 27 May 2008 23:25:57 +0200 (CEST)


Dear all,

I stumbled over a problem recently when trying to use srt with text() on a windows device.

What I intended to do was to plot a simple regression line, and to rotate a piece of text such that the text has the same angle as the regression line.

However, the text is always plotted in a slightly wrong angle:

####

x=1:10 #create arbitrary x and y values y=x*2-rnorm(1:10)

plot(x,y,pch=16,xlim=c(0,10)) #create the graph abline(lm(y~x))

#calculate the y coordinate of the text:
yval=predict(lm(y~x),list(x=rep(2,length(x))))[1]

#calculate the slope:

slope=as.numeric(lm(y~x)[[1]][2])

text(2,yval,"Regression",srt=180/pi*atan(slope),adj=0)

####

What am I doing wrong here?

Many thanks in advance for any help!

Best wishes
Christoph

(using R 2.6.1 on Windows XP)



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