[R] Determine area between two density plots

[Peter Alspach]

Tena koe Ralf

If you save the results of density()

x1Den <- density(x1)

you get the x and y values of the line which is plotted.  Similarly for x2 - you can then use these to shade the joint area and find the area.  Tinkering with the arguments of density to make the x values for each the same will make this process easier.  Let me know if you'd like more details.

HTH ....

Peter Alspach

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Ralf B
> Sent: Thursday, 23 September 2010 8:55 a.m.
> To: r-help Mailing List
> Subject: [R] Determine area between two density plots
> 
> Hi group,
> 
> I am creating two density plots as shown in the code below:
> 
> x1 <- c(1,4,5,3,2,3,4,5,6,5,4,3,2,1,1,1,2,3)
> x2 <- c(1,4,5,3,5,7,4,5,6,1,1,1,2,1,1,1,2,3)
> plot(density(x1, na.rm = TRUE))
> polygon(density(x2, na.rm = TRUE), border="blue")
> 
> How can I determine the area that is covered between the two plots as
> a number and how can I grey (or highlight with a pattern) the area
> that lies between the two lines?
> 
> Thanks,
> Ralf
> 
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