On Monday 04 April 2005 13:22, Rajarshi Guha wrote: > Hi, > I have a set of x,y data points and each data point lies between > (0,0) and (1,1). Of this set I have selected all those that lie in > the lower triangle (of the plot of these points). > > What I would like to do is to divide the region (0,0) to (1,1) into > cells of say, side = 0.01 and then count the number of cells that > contain a point. > > My first approach is to generate the coordinates of these cells and > then loop over the point list to see whether a point lies in a cell > or not. > > However this seems to be very inefficient esepcially since I will > have 1000's of points. > > Has anybody dealt with this type of problem and are there routines to > handle it?
A combination of cut and table/xtabs should do it, e.g.: x <- runif(3000) y <- runif(3000) fx <- cut(x, breaks = seq(0, 1, length = 101)) fy <- cut(y, breaks = seq(0, 1, length = 101)) txy <- xtabs(~ fx + fy) image(txy > 0) sum(txy > 0) Deepayan ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html