to2DArray() {
                var copy = new Array(this.rows);
                for (var i = 0; i < this.rows; i++) {
                    copy[i] = new Array(this.columns);
                    for (var j = 0; j < this.columns; j++) {
                        copy[i][j] = this.get(i, j);
                    }
                }
                return copy;
            }
Returns a 2D array containing a copy of the data
@return {Array}