[R] question on graphs and finding area under a curve

[Marc Schwartz]

On Tue, 2005-08-02 at 18:20 +0530, Renuka Sane wrote:
> Question on graphs:
> 
> The default case for drawing a graph in R, is where a little space is left 
> on the x and y axis before the first tick i.e. even if I say xlim=c(0,1) -- 
> there will be some space between the edge of the x-axis and where 0 is 
> placed. If I want 0 on the edge, how do I do it in R?

See ?par and take note of the 'xaxs' and 'yaxs' parameters. By default,
these are set to 'r', where the axes are extended by 4% in each
direction. Thus, set one or both parameters to 'i' to set the axes to
exactly the ranges of xlim and/or ylim as you require.

> Area under the curve:
> 
> I have a 45 degree line and a curve above or below it. Is there a way in R 
> to find the area between the two?

See Frank Harrell's somers2() function in the Hmisc package on CRAN.
Among other things, it outputs a value "C", which is the AUC.

HTH,

Marc Schwartz