thank you, Petr. This is exactly what I'm looking for in my post. An related question can be how to get an arbitrary weight, say if row1 and row 2 have 1 common value 1, then assign a weight 10, if row 1 and row 2 have 2 common value 1, then assign a weight 12. I'm not so sure how to expand your method. Really need to refresh my linear algebra;-) regards, cal@cowbo
On 6/14/12, Petr Savicky <savi...@cs.cas.cz> wrote: > 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. > ______________________________________________ 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.
