row() gives the row number of each element of the matrix, similarly col() gives the column number. By definition, diagonal elements are the elements correspond to same row and column numbers. That's how it works...
x <- matrix(1:12, 3, 4) > x [,1] [,2] [,3] [,4] [1,] 12 9 6 3 [2,] 11 8 5 2 [3,] 10 7 4 1 > row(x) [,1] [,2] [,3] [,4] [1,] 1 1 1 1 [2,] 2 2 2 2 [3,] 3 3 3 3 > col(x) [,1] [,2] [,3] [,4] [1,] 1 2 3 4 [2,] 1 2 3 4 [3,] 1 2 3 4 -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of onyourmark Sent: Tuesday, April 21, 2009 6:03 PM To: r-help@r-project.org Subject: Re: [R] search through a matrix Thanks very much. I don't really understand the row() function. I looked in the reference but I don't really get it. It says: Description Returns a matrix of integers indicating their row number in a matrix-like object, or a factor indicating the row labels. Usage row(x, as.factor = FALSE) Arguments x a matrix-like object, that is one with a two-dimensional dim. I don't understand what row() does. And in the example in the documentation it says: x <- matrix(1:12, 3, 4) # extract the diagonal of a matrix dx <- x[row(x) == col(x)] dx [1] 1 5 9 I thought the single square bracket notation accepts a pair separated by a comma but I don't see how row(x)==col(x) produces that? Thanks again. onyourmark wrote: > > Hi. I have a 925 by 925 correlation matrix corM. I want to identify all > variables that have correlation greater than 0.9. Can anyone suggest an > "R way" of doing this? > > Thank you. > -- View this message in context: http://www.nabble.com/search-through-a-matrix-tp23153538p23155104.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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. This e-mail may contain confidential and/or privileged i...{{dropped:10}} ______________________________________________ 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.