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.