Re: [R] help in density estimation
There was a typo error in my code below. See the inserted correction. On 23-Sep-10 17:05:45, Ted Harding wrote: > On 23-Sep-10 16:52:09, Duncan Murdoch wrote: >> On 23/09/2010 11:42 AM, wangguojie2006 wrote: >>> b<-runif(1000,0,1) >>> f<-density(b) >> >> f is a list of things, including x values where the density is >> computed, >> and y values for the density there. So you could do it by linear >> interpolation using approx or approxfun. For example >> >> > b <- runif(1000,0,1) >> > flist <- density(b) >> > f <- approxfun(flist$x, flist$y) >> > f(0.2) >> [1] 0.9717893 >> > f(-1) >> [1] NA >> >> If you don't like the NA for an out-of-range argument, then choose >> something different from the default for the "rule" argument to >> approxfun. >> >> Duncan Murdoch > > Or, perhaps more transparently (and more explicitly modifiable): b<-runif(1000,0,1) f <- density(b, from=0, to=1, n=512) plot(f$x, f$y, type="l", col="blue", xlim=c(0,1), ylim=c(0,1.5)) ## Plot the density estimate x0 <- 0.5## Target value of x i0 <- max(which(f$x <= x0)) i1 <- min(which(f$x > x0)) ##u0 <- f$x[i0] ; v0 <- f$y[i1]## WRONG! u0 <- f$x[i0] ; v0 <- f$y[i0]## Correction u1 <- f$x[i1] ; v1 <- f$y[i1] y0 <- v0 + (v1-v0)*(x0-u0)/(u1-u0) ## Linear interpolation points(x0, y0, pch="+", col="red") ## Add interpolated point > Ted. > > > E-Mail: (Ted Harding) > Fax-to-email: +44 (0)870 094 0861 > Date: 23-Sep-10 Time: 18:05:41 > -- XFMail -- E-Mail: (Ted Harding) Fax-to-email: +44 (0)870 094 0861 Date: 23-Sep-10 Time: 20:38:53 -- 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.
Re: [R] help in density estimation
You guys are really good. Thanks. -- View this message in context: http://r.789695.n4.nabble.com/help-in-density-estimation-tp2552264p2552484.html Sent from the R help mailing list archive at Nabble.com. __ 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.
Re: [R] help in density estimation
You could do: b <- runif(1, 0, 1) tmp <- density(b, from=0.5, to=0.5, n=1) tmp$y As one direct approach. You could also look at the logspline package for an alternative for density estimation that provides you with a density function (and also allows for finite domains). -- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare greg.s...@imail.org 801.408.8111 > -Original Message- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r- > project.org] On Behalf Of wangguojie2006 > Sent: Thursday, September 23, 2010 9:43 AM > To: r-help@r-project.org > Subject: [R] help in density estimation > > > Hi, guys, > > I'm using kernel "density" estimation. But how can I return to a > density > estimation for a fixed point? > > For example, > > b<-runif(1000,0,1) > f<-density(b) > > How can I get the value of density(b) at b=0.5? > > Your help is extremely appreciated. Thanks. > > Jay > -- > View this message in context: http://r.789695.n4.nabble.com/help-in- > density-estimation-tp2552264p2552264.html > Sent from the R help mailing list archive at Nabble.com. > > __ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting- > guide.html > and provide commented, minimal, self-contained, reproducible code. __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] help in density estimation
On 23-Sep-10 16:52:09, Duncan Murdoch wrote: > On 23/09/2010 11:42 AM, wangguojie2006 wrote: >> b<-runif(1000,0,1) >> f<-density(b) > > f is a list of things, including x values where the density is > computed, > and y values for the density there. So you could do it by linear > interpolation using approx or approxfun. For example > > > b <- runif(1000,0,1) > > flist <- density(b) > > f <- approxfun(flist$x, flist$y) > > f(0.2) > [1] 0.9717893 > > f(-1) > [1] NA > > If you don't like the NA for an out-of-range argument, then choose > something different from the default for the "rule" argument to > approxfun. > > Duncan Murdoch Or, perhaps more transparently (and more explicitly modifiable): b<-runif(1000,0,1) f <- density(b, from=0, to=1, n=512) plot(f$x, f$y, type="l", col="blue", xlim=c(0,1), ylim=c(0,1.5)) ## Plot the density estimate x0 <- 0.5## Target value of x i0 <- max(which(f$x <= x0)) i1 <- min(which(f$x > x0)) u0 <- f$x[i0] ; v0 <- f$y[i1] u1 <- f$x[i1] ; v1 <- f$y[i1] y0 <- v0 + (v1-v0)*(x0-u0)/(u1-u0) ## Linear interpolation points(x0, y0, pch="+", col="red") ## Add interpolated point Ted. E-Mail: (Ted Harding) Fax-to-email: +44 (0)870 094 0861 Date: 23-Sep-10 Time: 18:05:41 -- XFMail -- __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] help in density estimation
On 23/09/2010 11:42 AM, wangguojie2006 wrote: b<-runif(1000,0,1) f<-density(b) f is a list of things, including x values where the density is computed, and y values for the density there. So you could do it by linear interpolation using approx or approxfun. For example > b <- runif(1000,0,1) > flist <- density(b) > f <- approxfun(flist$x, flist$y) > f(0.2) [1] 0.9717893 > f(-1) [1] NA If you don't like the NA for an out-of-range argument, then choose something different from the default for the "rule" argument to approxfun. Duncan Murdoch __ 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.
