6.4.2 Turn a set of arrays into a StarTable

Suppose you have three arrays representing a set of points on the plane, giving an index number and an x and y coordinate, and you would like to manipulate them as a StarTable. One way is to use the ColumnStarTable class, which gives you a table of a specified number of rows but initially no columns, to which you can add data a column at a time. Each added column is an instance of ColumnData; the ArrayColumn class provides a convenient implementation which wraps an array of objects or primitives (one element per row).

    StarTable makeTable( int[] index, double[] x, double[] y ) {
        int nRow = index.length;
        ColumnStarTable table = ColumnStarTable.makeTableWithRows( nRow );
        table.addColumn( ArrayColumn.makeColumn( "Index", index ) );
        table.addColumn( ArrayColumn.makeColumn( "x", x ) );
        table.addColumn( ArrayColumn.makeColumn( "y", y ) );
        return table;
    }

A more general way to approach this is to write a new implementation of StarTable; this is like what happens in Swing if you write your own TableModel to provide data for a JTable. In order to do this you will usually want to subclass one of the existing implementations, probably AbstractStarTable, RandomStarTable or WrapperStarTable. Here is how it can be done:

    class PointsStarTable extends RandomStarTable {

        // Define the metadata object for each of the columns.
        ColumnInfo[] colInfos_ = new ColumnInfo[] {
            new ColumnInfo( "Index", Integer.class, "point index" ),
            new ColumnInfo( "X", Double.class, "x co-ordinate" ),
            new ColumnInfo( "Y", Double.class, "y co-ordinate" ),
        };

        // Member variables are arrays holding the actual data.
        int[] index_;
        double[] x_;
        double[] y_;
        long nRow_;

        public PointsStarTable( int[] index, double[] x, double[] y ) {
            index_ = index;
            x_ = x;
            y_ = y;
            nRow_ = (long) index_.length;
        }

        public int getColumnCount() {
            return 3;
        }

        public long getRowCount() {
            return nRow_;
        }

        public ColumnInfo getColumnInfo( int icol ) {
            return colInfos_[ icol ];
        }

        public Object getCell( long lrow, int icol ) {
            int irow = checkedLongToInt( lrow );
            switch ( icol ) {
                case 0: return new Integer( index_[ irow ] );
                case 1: return new Double( x_[ irow ] );
                case 2: return new Double( y_[ irow ] );
                default: throw new IllegalArgumentException();
            }
        }
    }