docs: protected static <A> int size(NumberArrayAdapter<?, A> adapter, Collection<? extends A> data) {
      if(data.size() < 2) {
        throw new IllegalArgumentException("Need at least two axes to compute dependence measures.");
      }
      Iterator<? extends A> iter = data.iterator();
      final int len = adapter.size(iter.next());
      while(iter.hasNext()) {
        if(len != adapter.size(iter.next())) {
          throw new IllegalArgumentException("Array sizes do not match!");
        }
      }
      if(len == 0) {
        throw new IllegalArgumentException("Empty array!");
      }
      return len;
    }