How to compute the 90° percentile in an Aggregate Operator

There might be situations where it is necessary to enhance the functionalties of the out-of-the-box StreamBase aggregation operations. In particular, in aviation it's very common to compute the 90th percentile of the velocity. This can be done by adding a StreamBase Custom Java Aggregate Function like the following:

//
// Copyright (c) 2009-2014 TIBCO Software Inc. All rights reserved.
//
package com.tibco.sb.math;

import org.apache.commons.math3.stat.descriptive.DescriptiveStatistics;
import com.streambase.sb.operator.AggregateWindow;
/**
 * Java custom aggregate that returns the 90° Percentile in a window. 
 * 
 */
@SuppressWarnings("serial")
public class Percentile90 extends AggregateWindow {
    // Get a DescriptiveStatistics instance
    DescriptiveStatistics stats = null;

    public void init() {
        // Get a DescriptiveStatistics instance
        stats = new DescriptiveStatistics();
    }

    public Double calculate() {
        return new Double(stats.getPercentile(90));     
    }

    public void accumulate(double val) {
        stats.addValue(val);
    } 
}

This function is based on the org.apache.commons.math3.stat library. Once compiled, the enhancement can be used in an Aggregate Operator as shown below.