Suggestion 1: Use the R function `dist'. Suggestion 2: Don't mask an R system function name.
Suggestion 3: Time this. I don't think it is worth vectorizing. Suggestion 4: The bit which is actually nonvectorized is your function dist. If you had a vectorized distance function, you could do for(i in 1:5) array[i,] <- dist(a[i,,drop=FALSE] , a) but that would need dist <- function(x1,x2) sqrt(rowSums(x1-x2)^2) I could tell you how to fully vectorize it, but I doubt if it would have any benefit. (None of this is tested, because of 1 and 3.) On Tue, 25 May 2004, Robin Hankin wrote: > Hi guys. Another thing I cannot vectorize: > > I have an array "a", of size 5-by-2, for example, of 5 2D vectors. I > also have a distance function that computes the distance between two > vectors (usual Euclidean distance is a good example but I have other metrics I > want to use as well). I want a 5-by-5 array with the [i,j]th element being > the distance from a[i,] to a[j,] > > To Wit: > > a <- matrix(1:10,5,2) > array <- matrix(NA, 5, 5) > dist <- function(x1,x2){sqrt(sum(x1-x2)^2)} > > #NONVECTORIZED BIT FOLLOWS > for(i in 1:5) { > for(j in 1:5) { > array[i,j] <- dist(a[i,] , a[j,]) > } > } > > (note that array[i,i]=0 for i=1:5 as expected). > > How to vectorize this? > > > -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html