Column and Row Identification in a Matrix
DESCRIPTION:
Returns a matrix filled with integers each of which is the row or column number in which it resides.
USAGE: 
col(x)
row(x)
REQUIRED ARGUMENTS:
x:
matrix. Missing values (NAs) are allowed.
VALUE:
integer matrix, containing the row number or column number of each element. If z<-row(x), z[i,j] is i for all j; if z<-col(x), z[i,j] is j for all i.
NOTE:
Do not confuse this function with the col parameter in graphics functions; see par for that use of col.
SEE ALSO:
diag , ncol , slice.index .
EXAMPLES: 
x[row(x)>col(x)] <- 0     # zero the strict lower triangle of x
x[row(x)-col(x)==1]     # first sub-diagonal