/**
 * Clears the series at the given positions, so the graph won't 
 * be shown anymore.
 * 
 * @param diagram:
 * The diagram containing the series to clear.
 * 
 * @param clearIndex:
 * The positions of the series that shall be cleared
 */
function clearSeriesOfDiagram (diagram, clearIndex) {
   /* ======================================== */
   // get the dataset
   var dataset = diagram.getChart().getXYPlot().getDataset();
 
   // clear all series of the dataset at the given positions
   for (var index = 0; index < clearIndex.length; index++) {
      dataset.getSeries(clearIndex[index]).clear();
   }
   /* ======================================== */
}