[R] Area of density

[Rolf Turner]

On 6/09/2008, at 8:32 AM, pragmatic wrote:

>
> Hello!
> Please, anybody help me.
>
> Can I calculate area of density was created by:
>> D <- density(x)
> In other words I want to know area under curve 'plot(D)'
> and It's good to calculate area before and after 0 separately.

(1) You could use splinefun()

	foo <- splinefun(D$x,D$y)
	integrate(foo,min(D$x),0)
	integrate(foo,0,max(D$x))

or you could use simp() from

	http://finzi.psych.upenn.edu/R/Rhelp02a/archive/134918.html

	with(D,simp(y=y[x<0],x=x[x<0]))
	with(D,simp(y=y[x>0],x=x[x>0]))

You'll get different answers, neither of which is ``correct''.

	cheers,

		Rolf Turner

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