Just try to run x[row(x) == col(x)] . You'll see it's a vector. It's the same as diag(x) Dimitri
On Tue, Apr 21, 2009 at 9:02 AM, onyourmark <william...@gmail.com> wrote: > > Hi again. Thanks. I get it now. > So row(x) is a matrix with just the row number for each entry. > > How about x[row(x) == col(x)] ? > Can the square bracket function take a matrix as its argument? If so, I > guess I understand this statement. > The argument is a boolean matrix. > > Thank you. > > > David Winsemius wrote: >> >> >> On Apr 21, 2009, at 8:33 AM, onyourmark wrote: >> >>> >>> 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. >> >> It returns a matrix of the same size as its arguments populated with >> the row numbers instead of the matrix elements. >>> >>> >>> And in the example in the documentation it says: >>> x <- matrix(1:12, 3, 4) >> >> Now try row(x) >> >>> >>> # 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? >> >> The single square bracket notation can be used as [r,c] or without >> the comma which requires a logical index. In the second method the >> matrix entries get processed serially, column-wise. >> >> > x <- matrix(1:12, 3, 4) >> > x[TRUE] >> [1] 1 2 3 4 5 6 7 8 9 10 11 12 >> > row(x) >> [,1] [,2] [,3] [,4] >> [1,] 1 1 1 1 >> [2,] 2 2 2 2 >> [3,] 3 3 3 3 >> >> -- >> David Winsemius, MD >> Heritage Laboratories >> West Hartford, CT >> >> ______________________________________________ >> 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. >> >> > > -- > View this message in context: > http://www.nabble.com/search-through-a-matrix-tp23153538p23155615.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. > -- Dimitri Liakhovitski MarketTools, Inc. dimitri.liakhovit...@markettools.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.
