protected ResultSet getChartData() {
// make a copy of the data that only includes the columns of interest
ResultSet chartData = histData.getResultSet().pluckColumns(xColumn,
methodPurpose.getYColumn());
// discard any rows that have zeros in the X or Y value
for (int row = chartData.numRows(); row > 0; row--) {
if (!goodChartData(chartData.getData(row, 1))
|| !goodChartData(chartData.getData(row, 2)))
chartData.removeRow(row);
}
return chartData;