[R] srt --- slope text with function?

[Duncan Murdoch]

On 2/4/2006 3:50 PM, ivo welch wrote:
> [resent, plus small addition; I do not understand why gmail sent a
> weird charset.]
> 
> Dear R wizards:
> 
> I would love to write a general function that matches the slope of a plotted
> line in an xy-plot at a particular x,y location.  something like
> 
>    x<- (1:10)^2; y<- 40:50;
>    plot( x,y, type="l", xlim=c(0,90) )
>    srt.at5 = text.at.current.plot.with.slope( x, y,  5);
>    text( x[5],y[5], pos=3, srt=srt.at.5);
> 
> to do this, I first need to compute the function slope around x[5], which is
> an easy task.  alas, the harder task is that I need to scale this by the
> plot aspect ratio and the axes.  How can a function read this from the
> current plot?

I haven't done this, but you can presumably work it out from the 
conversions implied by the "fig", "fin", "plt", and/or "usr" values.
> 
> (Has someone written such a function, perhaps more embellished, to save me
> the debugging effort?)
> 
> Or, is there an alternative to srt, which slopes the text relative to the
> existing scale?
> 
>   *** come to think of it, what I would really like is the ability of
> text to 'snake' itself along the line itself.  I doubt that this is
> easily possible, but I just wanted to ask.

Using strsplit and strwidth you should be able to do it, but it will 
probably look quite ugly.

Duncan Murdoch