The problem with David's proposal is revealed by: mat[7:1,] # [,1] [,2] [,3] # [1,] 7 14 21 # [2,] 6 13 20 # [3,] 5 12 19 # [4,] 4 11 18 # [5,] 3 10 17 # [6,] 2 9 16 # [7,] 1 8 15
which simply reverses the rows. Then: c(mat[7:1,]) # [1] 7 6 5 4 3 2 1 14 13 12 11 10 9 8 21 20 19 18 17 16 15 since a matrix is stored "by columns" -- i.e. as a vector with its elements ordered down each column, per col1 then col2 then ... And the following won't work either: mat[,1:3] # [,1] [,2] [,3] # [1,] 1 8 15 # [2,] 2 9 16 # [3,] 3 10 17 # [4,] 4 11 18 # [5,] 5 12 19 # [6,] 6 13 20 # [7,] 7 14 21 which is simply the original matrix, and hence: c(mat[,1:3]) # [1] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 for the same reson as before. What you need to do is based on the following: t(mat[7:1,]) # [,1] [,2] [,3] [,4] [,5] [,6] [,7] # [1,] 7 6 5 4 3 2 1 # [2,] 14 13 12 11 10 9 8 # [3,] 21 20 19 18 17 16 15 which now has the elements (down the columns) in the order you want. So: c(t(mat[7:1,])) # [1] 7 14 21 6 13 20 5 12 19 4 11 18 3 10 17 2 9 16 1 8 15 As desired. Ted. On 23-Aug-09 18:53:38, Bogaso wrote: > > No no, I actually want following result : > > 7, 14, 21, 6, 13, 20, 5, 12, 19,............ > > > > > David Winsemius wrote: >> >> >> On Aug 23, 2009, at 2:37 PM, Bogaso wrote: >> >>> >>> I have suppose a matrix like that >>> >>>> mat <- matrix(1:21, 7) >>>> mat >>> [,1] [,2] [,3] >>> [1,] 1 8 15 >>> [2,] 2 9 16 >>> [3,] 3 10 17 >>> [4,] 4 11 18 >>> [5,] 5 12 19 >>> [6,] 6 13 20 >>> [7,] 7 14 21 >>> >>>> From this matrix, I want to create a vector like tha : >>> >>> c(mat[7,], mat[6,], mat[5,], ....., mat[1,]) >>> >>> Can anyone please guide me, how to do that? >> >> c( mat[7:1,] ) >> >> # [1] 7 6 5 4 3 2 1 14 13 12 11 10 9 8 21 20 19 18 17 16 15 >> >> -- >> >> 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/A-matrix-calculation-tp25106048p25106224.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. -------------------------------------------------------------------- E-Mail: (Ted Harding) <ted.hard...@manchester.ac.uk> Fax-to-email: +44 (0)870 094 0861 Date: 23-Aug-09 Time: 20:17:58 ------------------------------ XFMail ------------------------------ ______________________________________________ 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.