vr your code is superior than the long code I have posted!

If I may add: using oddpctover() might be preferred because it does not interpolate when there is no data at the exact percentile position.

Regarding the time difference when running with and without "use threads", I have discovered that avg() is the culprit. If you use x-> index( $idx )->at(0) rather than x-> index( $idx )->avg the performance is the same (which means idx() is also excluded as possible cause).