[R] search through a matrix

[David Winsemius]

On Apr 21, 2009, at 9:02 AM, onyourmark wrote:

>
> Hi again. Thanks. I get it now.
> So row(x) is a matrix with just the row number for each entry.

Yes.
>
>
> 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.

It can and it often does. The argument to the [] operation can be  
either a logical vector or a numeric vector which gets treated as an  
index. Try x[8]. My understanding is that the matrix, row(x) ==  
col(x), as an argument would first get coerced to a vector constructed  
from the column-wise projection of the matrix. You can read further on  
the help page in the section that discusses matrices and arrays:

?"["
>

David Winsemius, MD
Heritage Laboratories
West Hartford, CT