[R] problem with abline for x.y

[Deepayan Sarkar]

On Friday 20 February 2004 08:17, Michael Friendly wrote:
> I'm trying to do a sunflowerplot of Galton's data, with both regression
> lines and data ellipses,
> and I must be doing something wrong, because the lines do not intersect
> at \bar{x}, \bar{y}.
> The problem is likely in the line for x.y, but I don't know how to
> specify that correctly.

[...]

> # both attempts plot the same, wrong regression lines
> y.x <- lm(parent ~ child, weights=frequency)
> abline(y.x)
> x.y <- lm(child ~ parent, weights=frequency)
> abline(x.y, col="gray")
>
> attach(galton2)
> y.x <- lm(parent ~ child)
> abline(y.x, lwd=2)
> x.y <- lm(child ~ parent)
> abline(x.y, col="gray", lwd=2)

This looks like you are getting a line with equation of the form 

x = c0 + c1 y

and then plotting the line 

y = c0 + c1 y

You should probably do 

cx.y <- coef(x.y)
cx.y <- c(-cx.y[1], 1) / cx.y[2]

abline(cx.y)

[Code untested, though]

Deepayan