[R-sig-eco] lines() adds extra line

[Jane Shevtsov]

I'm trying a bit of an experiment with polynomial curve fitting (don't
worry, I wouldn't do this to actual data -- it's just a toy model for
a specific question). When I generate a linear model of the data and
plot it using plot(), everything works fine. But when I use plot(...,
type="l") or lines(), I get an extra line connecting two points. How
do I stop this from happening?

Here's the code:
x = seq(-10, 10, by=0.1)
data1poly <- 0.1*x + 0.2*x^2 + 0.3*x^3 + 0.4*x^4 + 0.5*x^5 + 0.6*x^6 +
0.7 + rnorm(length(x),1E-3, 1E-4)
data2poly <- 0.1*x + 0.2*x^2 + 0.3*x^3 + 0.4*x^4 + 0.5*x^5 + 0.6*x^6 -
1 + rnorm(length(x), 1E-3, 1E-4)
dataBoth.poly <- c(data1poly, data2poly)
#Works well
plot(c(x,x), predict(lm(dataBoth.poly ~ c(x,x) +
I(c(x,x)^2)+I(c(x,x)^3)+I(c(x,x)^4)+I(c(x,x)^5)+I(c(x,x)^6))))
#Adds extra line
plot(c(x,x), predict(lm(dataBoth.poly ~ c(x,x) +
I(c(x,x)^2)+I(c(x,x)^3)+I(c(x,x)^4)+I(c(x,x)^5)+I(c(x,x)^6))),
type="l")  #or
lines(c(x,x), predict(lm(dataBoth.poly ~ c(x,x) +
I(c(x,x)^2)+I(c(x,x)^3)+I(c(x,x)^4)+I(c(x,x)^5)+I(c(x,x)^6))))

Thanks,
Jane

-- 
-------------
Jane Shevtsov
Ecology Ph.D. candidate, University of Georgia
co-founder, <www.worldbeyondborders.org>
Check out my blog, <http://perceivingwholes.blogspot.com>Perceiving Wholes

"The whole person must have both the humility to nurture the
Earth and the pride to go to Mars." --Wyn Wachhorst, The Dream
of Spaceflight