code: public Percentile percentileDisc(Number percentile) {
  		ReturnExpression rx = getReturnExpression();
  		ReturnAggregate ra = (ReturnAggregate) rx.getReturnValue();
  		ra.setType(AggregateFunctionType.PERCENTILE_DISC);
  		ra.setPercentile(percentile);
  		Percentile ret = new Percentile(rx);
  		return ret;
  	}
docs: <div color='red' style="font-size:24px;color:red"><b><i><u>JCYPHER</u></i></b></div>
  <div color='red' style="font-size:18px;color:red"><i>calculate: Given a series of values, which value is located at (or nearest to) a certain percentile (percent rank);</b></i></div>
  <div color='red' style="font-size:18px;color:red"><i>takes the percentile (between 0.0 and 1.0)</i></div>
  <div color='red' style="font-size:18px;color:red"><i>e.g. ...aggregate().<b>percentileDisc(0.5)</b>...</i></div>
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