The power.examp function in the TeachingDemos package (among others) may already do what you want. Even if it does not, it does shade the area under a curve, you can look at the source for the function as an example of where to start.
Hope this helps, -- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare [EMAIL PROTECTED] (801) 408-8111 > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Bertolt Meyer > Sent: Thursday, August 28, 2008 8:03 AM > To: r-help@r-project.org > Subject: [R] Help with shading a polygon below a segment of a > curve (normal distribution) > > Dear R users, > > I still feel new to R so please apologize if I am doing > something stupid here. My use of the polygon() function > produces a result that I cannot > comprehend: In a plot, I would like to shade the area below a > normal distribution. However, I do not want the entire area > to be shaded, but just the area on the right side of a > vertical line that I draw through the distribution (in order > to illustrate the function of a t-test). Here is what I do: > > scale <- 0.1 > x <- seq(-4, 6, scale) > y <- dnorm(x) > plot(x, y, type = "l", main="t-Test, t = 2.2") > > linepos <- 2.2 > abline(v = linepos) > > # I try to fill a polygon right of the vertical line: > # max(x) - linepos (in this case, 2.2) / scale (0.1) # > results in the last 38 elements of x and y. > # so I take the last 38 elements of x and y and try to # draw > a polygon underneath: > > cutpoint <- (max(x) - linepos) / scale > > xt <- x[(length(x)-cutpoint):length(x)] > yt <- y[(length(y)-cutpoint):length(y)] > > # draw the polygon > > polygon(xt, yt, density = 10 ) > > As you can see in the result, this is not what I want; some > area above the line gets shaded, but not below. Can someone > tell me what I am missing? > > Thank you very much, > Bertolt > > -- > Bertolt Meyer > Oberassistent > Sozialpsychologie, Psychologisches Institut der Universität > Zürich Binzmühlestr. 14, Box 15 CH-8050 Zürich > > [EMAIL PROTECTED] > tel: +41446357282 > fax: +41446357279 > mob: +41788966111 > > ______________________________________________ > 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.