Hello, If an N-dimensional convex hull fits your idea of a "smallest ball" then you could try the convhulln function in the geometry package.
For testing if a new point is inside a previously derived hull, one brute force approach is to rbind the new point to your data, generate a new hull and see if it is the same as the previous one. I've only used convhulln in low dimensions so I don't know how efficient it is when N is large. Hope this helps. Michael On 24 September 2010 19:44, Feng Li <feng...@stat.su.se> wrote: > Dear R, > > I have a covariates matrix with 10 observations, e.g. > >> X <- matrix(rnorm(50), 10, 5) >> X > [,1] [,2] [,3] [,4] [,5] > [1,] 0.24857135 0.30880745 -1.44118657 1.10229027 1.0526010 > [2,] 1.24316806 0.36275370 -0.40096866 -0.24387888 -1.5324384 > [3,] -0.33504014 0.42996246 0.03902479 -0.84778875 -2.4754644 > [4,] 0.06710229 1.01950917 -0.09325091 -0.03222811 0.4127816 > [5,] -0.13619141 1.33143821 -0.79958805 2.08274102 0.6901768 > [6,] -0.45060357 0.19348831 -1.23793647 -0.72440163 0.5057326 > [7,] -1.20740516 0.20231086 1.15584485 0.81777770 -1.2719855 > [8,] -1.81166284 -0.07913113 -0.91080581 -0.34774436 0.9552182 > [9,] 0.19131383 0.14980569 -0.37458224 -0.09371273 -1.7667203 > [10,] -0.85159276 -0.66679528 1.63019340 0.56920196 -2.4049600 > > And I define a boundary of X: The smallest "ball" that nests all the > observations of X. I wish to check if a particular point x_i > >> x_i <- matrix(rnorm(5), 1, 5) >> x_i > [,1] [,2] [,3] [,4] [,5] > [1,] -0.1525543 0.4606419 -0.1011011 -1.557225 -1.035694 > > is inside the boundary of X or not. I know it's easy to do it with 1-D or > 2-D, but I don't knot how to manage it when the dimension is large. > > Can someone give a hint? Thanks in advance! > > > Feng > > -- > Feng Li > Department of Statistics > Stockholm University > 106 91 Stockholm, Sweden > http://feng.li/ > > [[alternative HTML version deleted]] > > ______________________________________________ > 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.
