Calculate average top third of the population

Question

Could you guys help me which apache-commons-math classes can I use to calculate the average of the top third of the population.

To calculate the average I know can use org.apache.commons.math3.stat.descriptive.DescriptiveStatistics.

How to get the top third of the population?

Example

Population: 0, 0, 0, 0, 0, 1, 2, 2, 3, 5,14

Top third: 2, 3, 5, 14

Average = 24/4= 6.0

Answer 1

First of all what do you call top third of population? If set is divides by 3 and remainder is 0, then its is simple, but in your case 11%3 = 2. So You should know how to get top third when remainder is not equal 0.

I would suggest You to use Arrays procedures, to get Top third of set. If You still want to use DescriptiveStatistics you can invoke it.

    double[] set = {0, 0, 0, 0, 0, 1, 2, 2, 3,4,5};

    Arrays.sort(set);

    int from = 0;
    if (set.length % 3==0){
        from = set.length/3*2 ;
    }
    if (set.length % 3 != 0){
        from = Math.round(set.length/3*2) + 1;
    }

    double [] topThirdSet = Arrays.copyOfRange(set,from , set.length);
    DescriptiveStatistics ds = new DescriptiveStatistics(topThirdSet);
    System.out.println(ds.getMean());