@Override
    public boolean equals(Object obj) {
        if (this == obj) return true;
        if (obj == null) return false;
        if (getClass() != obj.getClass()) return false;
        FeatureNode other = (FeatureNode)obj;
        if (index != other.index) return false;
        if (Double.doubleToLongBits(value) != Double.doubleToLongBits(other.value)) return false;
        return true;
    }