string数组排序

想要对一个string数组排序
原来的数组是这样{"bb","bb","fff","a","ffff","c","dd","f","dd","e","dd"}
现在对这个数组进行排序，排序的规则是只出现一次的排在前面，出现2次及2次
以上的排在后面，那么就上面的数组排序后想要的结果就是
{"a","c","e","f","bb","bb","dd","dd","dd","fff","ffff"}

    protected void Button1_Click(object sender, EventArgs e)
    {
        string[] arr = { "bb", "bb","fff","a","ffff","c", "dd", "f", "dd", "e", "dd" };
        SortByCount(arr);
    }
    
    public void SortByCount(string[] source)
    {       
        Comparison<string> com = new Comparison<String>(function);
        Array.Sort<string>(source, com);        
    }

    int function(string s1, string s2)
    {
        return s1.Length - s2.Length == 0 ? string.Compare(s1, s2) : s1.Length - s2.Length;                
    }