Unique Random Sets description

This JavaScript, based on Unique Random Numbers II, picks Unique Random Sets. Here, there are more than one arrays (need not be of same length). First, we pick a number of unique random elements from the first array, numArr1 to form the array pickArr1. Now each element of pickArr1 picks another element from the second array numArr2, which again is unique and random. Thus we form the array pickArr2. Similarly each element of pickArr2 picks unique random elements from numArr3 to form pickArr3.