I have read your message four times in the last couple of days, but I still have very little idea what you want. Let's try some things I've gleaned. You have a matrix with 9 rows and 2 columns, and there is a 2 somewhere in column 1. > m <- matrix(1:18, nrow=9, ncol=2) > m[c(4,7,8),1] <- 2 > m [,1] [,2] [1,] 1 10 [2,] 2 11 [3,] 3 12 [4,] 2 13 [5,] 5 14 [6,] 6 15 [7,] 2 16 [8,] 2 17 [9,] 9 18 You want to select rows where column 1 is 2. > m[,1] == 2 [1] FALSE TRUE FALSE TRUE FALSE FALSE TRUE TRUE FALSE You want to select the corresponding elements from column 2. > m[m[,1] == 2, 2] [1] 11 13 16 17 You want the maximum of these elements. > max(m[m[,1] == 2, 2]) [1] 17
You can do pretty amazing things with indexing in R without any extra packages. Of course, I have almost certainly misunderstood you. Perhaps you can ask again, maybe with an example? On Fri, 21 Jun 2019 at 11:50, Vangelis Litos <redondo5_...@hotmail.com> wrote: > I am using R and I created based on a vector x, a grid (named: plain) - > where zero is included. This gives me a 9x2 ``matrix''. > > > x_t = cbind(c(1),c(2)); > > x = t(x_t); > > > plain = expand.grid (sort (unique (c (0, x))), sort (unique (c (0, x)))); > > My aim is to focus on column 1 and take i.e the first entry (then the > second, the third entry etc through a loop) of the unique (c (0, x)) vector > (==0) [rows 1, 4 and 7] and find the maximum value (entry) in the second > column of the matrix that satisfies a condition. > > Let say that the condition is satisfied when at column 2 the value is 2. > That is I want row 7 to be selected > > Then I want to create a column vector b (9x1) that has zero everywhere > apart from row 7. > > Can anybody help me with this? > > Thank you in advance. > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. > [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.