I think you need: dx2 <- exp(dx) dp2 <- dp / dx2 sum(c(0, diff(dx2)) * dp2)
I hope it helps. Best, Dimitris ---- Dimitris Rizopoulos Ph.D. Student Biostatistical Centre School of Public Health Catholic University of Leuven Address: Kapucijnenvoer 35, Leuven, Belgium Tel: +32/(0)16/336899 Fax: +32/(0)16/337015 Web: http://med.kuleuven.be/biostat/ http://www.student.kuleuven.be/~m0390867/dimitris.htm ----- Original Message ----- From: "Rainer M Krug" <[EMAIL PROTECTED]> To: "r-help" <[EMAIL PROTECTED]> Sent: Wednesday, January 16, 2008 10:34 AM Subject: [R] Question concerning pdfs > Hi > > I have a dataset of absolute growth rates g ranging from close to 0 > to > around whatever of which I want to calculate a pdf. > If I use density(g) the pdf will extend to below 0 so I logtransform > g > and do d <- density(log(g)). > Now I would like to transform this pdf back, i.e. d$x <- > exp(d$x) but what do I have to do with d$y? > > (below is a small example) > > Thanks for your help, > > Rainer > > > g <- exp(rnorm(100)) ## Just to generate the example data > > d <- density(log(g)) > dx <- d$x > dp <- d$y > > sum(c(0, (diff(dx))) * dp) ## this is equal to one > plot(dx, dp) > > dx2 <- exp(dx) > dp2 <- ??????? ## what should I do here? > > plot(dx2, dp2) ## what should I do here? > sum(c(0, (diff(exp(dx2)))) * dp2) ## this should be one > > > sum( c(0, (diff(dx2))) * ( dp1 / c(1, (diff(exp(dx2)))) * c(0, > (diff(dx1)))) ) ##This is obviously also one, but can > I > use this to define my dp2? i.e. > > dp2 <- dp1 / c(1, (diff(exp(dx2)))) * c(0, (diff(dx1)))) ###???? > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
