On Mon, 15 Aug 2005, Prof Brian Ripley wrote: > Probably you use the idea from unique.matrix, that is > > 1) form a string from each row and > 2) call match() to see which strings match your pattern row.
If your matrix A really does have short rows like c(1,2,3) and millions of them, another idea is to do target <- rep(c(1,2,3), each= nrow(A)) rowSums(A != target) == 0 For wider rows my first suggestion is probably faster. > On Sun, 14 Aug 2005, Todd Remund wrote: > >> I am looking for a fast way to count the number of rows in a matrix are >> identical to a pattern vector. For example, if I am interested in counting >> the number of row vectors in a matrix that are identical to (1,2,3) what >> would I do? I have tried the identical statement in a loop but this is far >> too slow. I have a very large matrix and need to avoid loops at all costs. -- 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://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
