read a sparse matrix, loading row and column name files. if
        specified, will add a prefix to the row or column names

def read(self, filename, rowprefix=None, colprefix=None, delim=":"):
        """read a sparse matrix, loading row and column name files. if
        specified, will add a prefix to the row or column names"""

        self.matrix = scipy.io.mmread(filename)
        with open(filename + ".rownames") as in_handle:
            self.rownames = [x.strip() for x in in_handle]
            if rowprefix:
                self.rownames = [rowprefix + delim + x for x in self.rownames]
        with open(filename + ".colnames") as in_handle:
            self.colnames = [x.strip() for x in in_handle]
            if colprefix:
                self.colnames = [colprefix + delim + x for x in self.colnames]