you could try the following: n <- nrow(X) k <- n * (n - 1) / 2 Y <- matrix(NA, k, n)
ind.up <- which(upper.tri(X), arr.ind = TRUE) ind.lo <- which(lower.tri(X), arr.ind = TRUE) Y[cbind(1:k, ind.lo[, 1])] <- X[ind.up] Y[cbind(1:k, ind.lo[, 2])] <- X[ind.lo] Y I hope it helps. Best, Dimitris ---- Dimitris Rizopoulos Ph.D. Student Biostatistical Centre School of Public Health Catholic University of Leuven Address: Kapucijnenvoer 35, Leuven, Belgium Tel: +32/(0)16/336899 Fax: +32/(0)16/337015 Web: http://med.kuleuven.be/biostat/ http://www.student.kuleuven.be/~m0390867/dimitris.htm ----- Original Message ----- From: "Robin Hankin" <[EMAIL PROTECTED]> To: "R program" <R-help@r-project.org> Sent: Wednesday, September 12, 2007 4:32 PM Subject: [R] vectorize a matrix conversion > Hello > > > I have X, an n-by-n matrix and want to convert it to Y, an > n(n-1)/2 -by- n matrix such that each row of Y > corresponds to an element of the upper diagonal > of X. Say row k of Y corresponds to [i,j] with i\neq j. > > Then Y[i,k] = X[i,j] and Y[j,k] = X[j,i]. > and Y[-c(i,j),k] = NA. > > How to do this vectorizedly? > > Example follows: > > > > > X > [,1] [,2] [,3] [,4] > [1,] NA 10 8 7 > [2,] 10 NA 7 12 > [3,] 12 13 NA 8 > [4,] 13 8 12 NA > > Y > [,1] [,2] [,3] [,4] > [1,] 10 10 NA NA > [2,] 12 NA 8 NA > [3,] 13 NA NA 7 > [4,] NA 13 7 NA > [5,] NA 8 NA 12 > [6,] NA NA 12 8 > > > > [matrix X corresponds to an all-play-all competition amongst 4 > individuals, > entry [i,j] corresponding to the number of times individual "i" won > when competing against individual "j". Thus individual 2 beat > individual > 3 seven times and individual 3 beat individual 2 thirteen times. > Note X[i,j] + X[j,i]=20 as there were 20 trials for each pair] > > > Pitiful nonvectorized code follows. > > n <- nrow(X) > Y <- matrix(NA,n*(n-1)/2,n) > k <- 1 > for(i in 1:(n-1)){ > for(j in (i+1):n){ > if( !(i==j)){ > print(c(i,j,k)) > Y[k,i] <- X[i,j] > Y[k,j] <- X[j,i] > } > k <- k+1 > } > } > > > > > > -- > Robin Hankin > Uncertainty Analyst > National Oceanography Centre, Southampton > European Way, Southampton SO14 3ZH, UK > tel 023-8059-7743 > > ______________________________________________ > 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. > Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm ______________________________________________ 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.
