A similar question was posed and answered:

http://finzi.psych.upenn.edu/R/Rhelp02a/archive/119793.html

Two aspects needed to be addressed ... specifying the same domain, and getting the x-values to "line up" prior to the subtraction (or whatever function is desired).

What are you going to do when the two functions cross?

 d1 <- dnorm(seq(-2,2,by=.1))
 d2 <- dnorm(seq(-2,2,by=.1), mean=2)
 plot(seq(-2,2,by=.1),d1)
 lines(seq(-2,2,by=.1),d2)

---- or----

 d4 <- dnorm(seq(-4,4,by=.1))
 d5 <- dnorm(seq(-4,4,by=.1), sd=5)
 plot(seq(-4,4,by=.1),d4)
 lines(seq(-4,4,by=.1),d5)

--
David Winsemius
On Dec 5, 2008, at 8:59 AM, Chang Jia-Ming wrote:

Dear all,

I wrote the following code to calculate the density functions for two data
sets, respectively.

 den_str <-density(str_data$Similarity);
 den_non_str <-density(nonstr_data$Similarity);

 However, I would like to knowing the difference between den_str and
den_non_str, that is, the difference between the region under the curve of
the den_str and the region under the curve of the den_non_str.

How to do?

Thank you for help.

Jia-Ming

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