@SuppressWarnings("unchecked")
private int getKeyForValue(float value) {
  Float2IntMap map = (Float2IntMap) _groupKeyMap;
  int groupId = map.get(value);
  if (groupId == INVALID_ID) {
    if (_numGroups < _globalGroupIdUpperBound) {
      groupId = _numGroups;
      map.put(value, _numGroups++);
    }
  }
  return groupId;
}