R plot: drawing only part of a linear regression line

Question

I can draw a partial linear regression line in a plot. For example a regression line for the last four values

sale5 <- c(6, 4, 9, 7, 6, 12, 8, 10, 9, 13)
plot(sale5)
abline(lsfit(tail(1:10,4), tail(sale5,4)))

But the regression line continues all the way back.

How can I draw only part of the regression line so that the regression line does not extending further back than four points in this case?

Thank you for your help.

Answer 1

I like to use ?clip for this sort of task:

plot(sale5)
clip(7,10,min(sale5),max(sale5))
abline(lsfit(tail(1:10,4), tail(sale5,4)))
# reset clipping to the extent of the plot region
do.call("clip", as.list(par("usr")))