[R] duplicate row.names

[John Smith]

I am looping over many data files and reading in the data with	 F <-
read.table(filename)	to read in a 22000 by 15 matrix.  Works fine on the
first matrix F, but I get the following error when the second file is read
into F:

Error in "row.names<-.data.frame"(*tmp*, value = row.names) : 
        duplicate row.names are not allowed

I have tried picking a column of the matrix and making that my rownames by
doing		rownames <- as.vector(F[,4])
-but that does not work.

Each row in my matrix is not unique.

Any suggestions greatly appreciated.

John