function.java

public <T> T applyFunction(String tenantId, MetricId id, long start, long end,
            Func1<Observable<DataPoint<Double>>, T> function) {
        Observable<DataPoint<Double>> dataPoints = metricsService.findGaugeData(tenantId, id, start, end);
        return function.call(dataPoints);
    }

    @Test
    public void getAverage() {
        DateTime start = now().minusMinutes(30);
        DateTime end = start.plusMinutes(20);
        String tenantId = "t1";
        MetricId id = new MetricId("m1");

        Observable<Double> avg = applyFunction(tenantId, id, start.getMillis(), end.getMillis(), dataPoints ->
            MathObservable.averageDouble(dataPoints.map(DataPoint::getValue))
        );
    }