[R] matrix problem

[David Winsemius]

On Jul 4, 2009, at 11:17 AM, William Simpson wrote:

> Can anybody please tell me a good way to do the following?
>
> Given a vector, number of rows and number of columns, return a matrix
> as follows. Easiest to give an example:
>
> x=c(1,2), nrow=5, ncol=4

You ought to separate those assignments with semicolons:

x=c(1,2); nrow=5; ncol=4
 > MM <- matrix( c(x,rep(0, nrow-length(x)+1)),  nrow=nrow, ncol=ncol)
Warning message:
In matrix(c(x, rep(0, nrow - length(x) + 1)), nrow = nrow, ncol =  
ncol) :
   data length [6] is not a sub-multiple or multiple of the number of  
rows [5]
 > MM
      [,1] [,2] [,3] [,4]
[1,]    1    0    0    0
[2,]    2    1    0    0
[3,]    0    2    1    0
[4,]    0    0    2    1
[5,]    0    0    0    2

OR------

 > M2 <- diag( , nrow=5, ncol=4)
 > M2[row(M2) == col(M2)+1] <- 2
 > M2
      [,1] [,2] [,3] [,4]
[1,]    1    0    0    0
[2,]    2    1    0    0
[3,]    0    2    1    0
[4,]    0    0    2    1
[5,]    0    0    0    2

>
> return the matrix:
>
>   1 0 0 0
>   2 1 0 0
>   0 2 1 0
>   0 0 2 1
>   0 0 0 2
>
> Thanks very much for any help!
> Bill
>
> ______________________________________________

David Winsemius, MD
Heritage Laboratories
West Hartford, CT