Question

I have an algorithm that calculates the percentile(85) with Apache Commons of a series of values (12 values), for a later evaluation with a threshold to make a decision. The result is similar to the one given by Excel, but not equal, and sometimes this is critical for my application because with excel the result doesn’t pass the threshold and with Apache Commons Math in Java it does, so I get different outputs.

Here it is an example: Internet traffic (Mbps) every 2 hours

32,7076813360000000 41,2580429776000000 45,4453940200000000 48,8044409456000000 46,7462847936000000 49,8028100056000000 54,3719451144000000 41,9708134600000000 29,4371963240000000 22,4667255616000000 20,0388452248000000 28,7807757104000000

After dividing by 1000 Mb (the capacity of the cable) I calculate the percentil(85) of the Occupation:

Excel: 0,049153870117

Apache Commons Math: 0.05003126676104001

I have found that it is possible to change the implementation of the percentile (it does not exist an official one) with setPercentileImpl(), but I couldn’t find any example of how to do this, or the Excel algorithm (which is the one I was told to achieve).

Any help about this will be welcomed.

Thank you.

Answer 1

The solution was creating a class PercentileExcel which is almost a copy of percentile from commons method except for a small change on how to caculate the position:

pos=(1+p*(n-1))/100;

Then you need to add this line to the code in order to use the new class for percentile:

setPercentileImpl(PercentileExcel);