Calculate weighted percentiles in a large data set

Hi! I'm i a new member on this board but I have been a visitor for long!


In my data set i have several items on my list ( somewhere in the range of 1000 items) that each of them has there own total weigh (n * 1000 kg).

Each of these items has also several contents (n mg/kg).


What I would like to know is how to calculate the weighted 80th percentile of each content for the total mass.


See my attached example file.