code: public JaccardIndex<K, VV, EV> setGroupSize(int groupSize) {
  		Preconditions.checkArgument(groupSize > 0, "Group size must be greater than zero");
  
  		this.groupSize = groupSize;
  
  		return this;
  	}
docs: Override the default group size for the quadratic expansion of neighbor
  pairs. Small groups generate more data whereas large groups distribute
  computation less evenly among tasks.
  
  <p>The default value should be near-optimal for all use cases.
  
  @param groupSize the group size for the quadratic expansion of neighbor pairs
  @return this