I would like to rearrange the matrix b in the following way:
> b <- matrix(1:24, 6, 4)
> b
[,1] [,2] [,3] [,4]
[1,] 1 7 13 19
[2,] 2 8 14 20
[3,] 3 9 15 21
[4,] 4 10 16 22
[5,] 5 11 17 23
[6,] 6 12 18 24
> cbind(b[1:2, ], b[3:4, ], b[5:6, ])
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12]
[1,] 1 7 13 19 3 9 15 21 5 11 17 23
[2,] 2 8 14 20 4 10 16 22 6 12 18 24
The number of rows (2 here) is always going to be the same but the matrix b is going to be very large, on the dimension of about 1M x 100. Is there some fast way I can do this without a for loop? Thanks.