On 21-Nov-10 19:11:20, William Dunlap wrote: >> -----Original Message----- >> From: r-help-boun...@r-project.org >> [mailto:r-help-boun...@r-project.org] On Behalf Of Shant Ch >> Sent: Saturday, November 20, 2010 6:34 PM >> To: David Winsemius >> Cc: r-help@r-project.org >> Subject: Re: [R] density at particular values >> >> David, I did look at ?density many times. I think I didn't >> explain what I have to find. >> >> Suppose I have a data. >> x<- c(rnorm(40,5,3),rcauchy(30,0,4),rexp(30,6)) >> >> Suppose I don't have information about the mixture, I have >> been given only the data. >> >> density(x) will give the 6 number summary of the data, given >> as x and also the 6 number summary of the density of density >> given as y. > > print(density(x)) displays a 6-number summary of the > x and y outputs of density, which are only tangentially > related to the data. (The default x output is a evenly > spaced seqence of n=512 values covering the range of > the input x.) I don't know why this display was chosen. > >> I want to find the density of the given data at x=1. I >> basically want the value >> of y(=density) for x=1 i.e. kernel density at x=1. > > If you really just want the density at a single > point, x0 (=1 in your case), you can do > d0 <- density(x, from=x0, to=x0, n=1)$y > (density only lets you choose the output x vector > as an evenly spaced sequence parameterized by > from, to, and n.) > > Bill Dunlap
Almost, but not quite! (Perhaps ... ). For example: set.seed(54321) x<- c(rnorm(40,5,3),rcauchy(30,0,4),rexp(30,6)) # Shant Ch's mixture min(x) # [1] -33.32023 max(x) # [1] 716.6736 d <- density(x,from=(-34),to=720,n=755) c(d$x[36],d$y[36]) ## Using density() on the full range of data # [1] 1.0000000 0.1125064 density(x,from=1,to=1,n=1)$y ## William's targeted density() # [1] 0.1136818 So there's about 1% difference in this example. Of course, what the answer *should* be is debatable, and 1% may be well within the debatable range, and William's 0.1136818 may be just as acceptable as my 0.1125064 (and that's without getting into issues of bandwidth and so on). I'm just putting it up to illustrate that you should not expect a "unique" answer to this question: what the answer is depends on how you set about finding it! Ted. -------------------------------------------------------------------- E-Mail: (Ted Harding) <ted.hard...@wlandres.net> Fax-to-email: +44 (0)870 094 0861 Date: 21-Nov-10 Time: 19:39:41 ------------------------------ XFMail ------------------------------ ______________________________________________ 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.