Bertolt, The points you send to polygon() do not fully enclose the area you desire. Try adding one more point as such
xt <- c(x[(length(x)-cutpoint):length(x)],linepos) yt <- c(y[(length(y)-cutpoint):length(y)],0) polygon(xt, yt, density = 10 ) -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Bertolt Meyer Sent: Thursday, August 28, 2008 9:03 AM To: r-help@r-project.org Subject: [R] Help with shading a polygon below a segment of a curve (normaldistribution) 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.