On Dec 4, 2013, at 8:56 AM, Duncan Murdoch wrote: > On 04/12/2013 11:36 AM, Jun Shen wrote: >> Hi, >> >> I have a dataset with two independent variables (x, y) and a response >> variable (z). I was hoping to generate a response surface by plotting x, y, >> z on a three dimensional plot. I can plot the data with rgl.points(x, y, >> z). I understand I may not have enough data to generate a surface. Is there >> a way to smooth out the data points to generate a surface? Thanks a lot. > > There are many ways to do that. You need to fit a model that predicts z from > (x, y), and then plot the predictions from that model. > An example below follows yours. >> >> Jun >> >> =========================== >> >> An example: >> >> x<-runif(20) >> y<-runif(20) >> z<-runif(20) >> >> library(rgl) >> rgl.points(x,y,z) > > Don't use rgl.points, use points3d() or plot3d(). Here's the full script: > > > x<-runif(20) > y<-runif(20) > z<-runif(20) > > library(rgl) > plot3d(x,y,z) > > fit <- lm(z ~ x + y + x*y + x^2 + y^2) >
Newcomers to R may think they would be getting a quadratic in x and y. But R's formula interpretation will collapse x^2 to just x and then it becomes superfluous and is discarded. The same result is obtained with z ~ (x + y)^2). I would have thought that this would have been the code: fit <- lm(z ~ poly(x,2) +poly(y,2) + x:y ) > xnew <- seq(min(x), max(x), len=20) > ynew <- seq(min(y), max(y), len=20) > df <- expand.grid(x = xnew, > y = ynew) > > df$z <- predict(fit, newdata=df) > > surface3d(xnew, ynew, df$z, col="red") With the modified fitting formula one sees a nice saddle (for that particular random draw) using rgl.snapshot(). The result with the earlier formula is a more restrained: Continued thanks to you Duncan for making this great tool available. -- David. > Duncan Murdoch >> David Winsemius Alameda, CA, USA ______________________________________________ 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.
