[R] Controlling the extent of ablines on plot

[Jerome Asselin]

On Tue, 2011-05-03 at 10:36 -0600, Ryan Utz wrote:
> Hi all,
> 
> I'm attempting to make a quite-specific plot where the axes cross at the
> origin and with gridlines for guidance. I've been using ablines to create
> the reference lines because I want a lot of control as to where they are
> placed on the axis. This command works very well for such control.
> However...
> 
> These ablines don't seem to work when I specify the origin as 0,0. They go
> beyond the x-axis at both ends, rendering a quite ugly graph (and they push
> back the y-axis title some).
> 
> Behold:
> 
> ###
> x<-c(0,1,2,3,4,5)
> y<-c(0,2,4,6,8,10)
> 
> plot(x,y, axes=FALSE)
> axis(1,at=c(0,1,2,2.5,3,4,5),pos=0)
> axis(2,at=c(0,2,4,6,8,10),pos=0)
> abline(h=c(1,2,3,4,5))
> ###
> 
> Is there any way for me to specify that these ablines should not go beyond
> the y-axis extent? I just want a pretty graph!
> 
> Thanks!
> Ryan
> 

Maybe you could use lines()?

plot(1:2)
lines(c(1,2),c(1.5,1.5))