On 19/06/2008, at 2:09 PM, Tariq Perwez wrote:
Hi
I just realized that when I use linear regression to draw a line
through my
data points with something like the following:
abline(lm(y ~ x))
the length of the line is infinite, i.e., the line goes beyond the
smallest
and the largest data values. This seems not very right to me (not
to mention
it looks unaesthetic). I do not mean to imply that the straight-line
behavior of my system is maintained throughout. I would like to
limit the
length of this line to the range of my data. However, I have not
been able
to figure out how to. Very disconcertingly, I found out that all
the books
that teach statistics using R seem to be drawing such infinite
length-lines.
I would appreciate any advice or suggestions.
As things stand, I don't think you can do it in one hit. You have to go
through something like
fit <- lm(y~x)
z <- predict(fit,data.frame(x=range(x)))
lines(range(x),z)
I guess one could ``automate'' this via something like:
fline <- function(object) {
# ``fline'' <--> fitted line.
r <- range(object$model[,2])
d <- data.frame(r)
names(d) <- attr(object$terms,"term.labels")
y <- predict(object,d)
lines(r,y)
}
(There may well be a cleverer way to do this .....)
And then execute
fline(lm(y~x))
Howzat?
cheers,
Rolf Turner
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