I think it would be very useful to add selectiveness and distinctiveness to pickset function.

Selectiveness by index range is simple using slice() function of Array object. But, selectiveness by items is not.
So, option for exclusion of some items, exclude would be convenient.

chance.pickset([1, 2, 3, 4, 5], 2, {exclude: [2, 4]});

Currently pickset function select items for the picked array distinctively from the given array. (If the given array has duplicate items at different positions, picked items can be duplicate, of course) But, sometimes it is necessary to pick multiple items allowing duplication (duplicate index, more exactly). So, option like distinct would be helpful.
The following code could produce array with duplicate values such as [2, 2].

chance.pickset([1, 2, ,3, 4, 5], 2, {distinct: false});