On Thu, Jun 14, 2012 at 01:11:45PM +0000, G. Dai wrote: > Dear Rlisters, > I'm writing to ask how to manipulate a matrix or dataframe in a specific way. > > To elaborate, let's consider an example. Assume we have the following > 3 by 4 matrix A with elements either 0 or 1, > 0 1 1 0 > 1 0 1 1 > 0 0 0 1 > > >From the original matrix A, I'd like to generate a new matrix B satisfing > 1) B is initially set to be equal to A, and then > 2) Each row of B is a weighted sum of rows of A > 3) The weight is given by the number of common 1 shared by the rows. > For row 1: > it has one common 1 with row 2, thus the weight is 1; > it has zero common 1 with row 3, thus the weight is 0; > For row 2: > it has one common 1 with row 1, thus the weight is 1; > it has one common 1 with row 3, thus the weight is 1; > For row 3: > it has zero common 1 with row 1, thus the weight is 0; > it has one common 1 with row 2, thus the weight is 1; > 4) In this way, the new matrix B is > 1 1 2 1 > 1 1 2 2 > 1 0 1 2
Hi. If i understand correctly, each row of B is obtained from the corresponding row of A by adding mutliples of other rows using the weights as described. Try the following. a <- rbind( c(0, 1, 1, 0), c(1, 0, 1, 1), c(0, 0, 0, 1)) w <- a %*% t(a) diag(w) <- 1 w %*% a [,1] [,2] [,3] [,4] [1,] 1 1 2 1 [2,] 1 1 2 2 [3,] 1 0 1 2 The entries of w are the weights except of the diagonal, which is all ones, since each row of A contributes to the same row of B with weight one. Is this, what you are looking for? Petr Savicky. ______________________________________________ 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.