Hi Petr, Sorry for the delay. I ended up implementing a simple and fast but not-universal or elegant solution, since it turned out that I only needed to test a rather small subset of combinations for my purposes.
Nevertheless, I did go back and try the solutions posted. Bill's 'binary expansion' approach was the fastest by about a factor of 8. Cheers, Kevin On Jan 11, 2011, at 9:20 AM, Petr Savicky wrote: > Dear Kevin Ummel: > > There were several suggestions on R-help concering your question below. > None of them suggests a base function. I would also expect that > there is a base function for matching the rows. A related function is > dist(), but it takes only one matrix as input and computes the distances > between all pairs of its rows. Matching only some rows would require > a modification of dist(), which would take two matrices and compare > rows of one of them to the rows of the other. However, i do not know > such a function in R. > > Is some of the suggestions on R-help suitable for your purposes? > > Thank you in advance for your kind reply. > > Best regards, Petr Savicky. > > On Wed, Jan 05, 2011 at 07:16:47PM +0000, Kevin Ummel wrote: >> Two posts in one day is not a good day...and this question seems like it >> should have an obvious answer: >> >> I have a matrix where rows are unique combinations of 1's and 0's: >> >>> combs=as.matrix(expand.grid(c(0,1),c(0,1))) >>> combs >> Var1 Var2 >> [1,] 0 0 >> [2,] 1 0 >> [3,] 0 1 >> [4,] 1 1 >> >> I want a single function that will give the row index containing an exact >> match with vector x: >> >>> x=c(0,1) >> >> The solution needs to be applied many times, so I need something quick -- I >> was hoping a base function would do it, but I'm drawing a blank. >> >> Thanks! >> Kevin >> >> ______________________________________________ >> 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.