如何为二阶马尔可夫链构建基于职业转换的数据结构？

我手头有一份记录个体不同年份就业状态的面板数据，不少个体在观测期内存在职业转换。我需要捕捉这些转换并开展二阶马尔可夫链分析——利用前两次的状态序列预测下一次转换的概率。为此，数据需要完成以下转换：

• 将连续的前两次就业状态合并为字符串序列（格式为「状态A-状态B」）
• 将该序列与下一次的就业状态并列展示

输入数据 #

Year Person Employment_Status
1990 Bob    High School Teacher 
1991 Bob    High School Teacher 
1992 Bob    Freelancer
1993 Bob    High School Teacher
1994 Bob    Researcher  
1990 Peter  Singer
1991 Peter  Singer
1990 John   Singer
1991 John   Dancer
1990 James  Actor
1991 James  Actor
1992 James  Producer
1993 James  Producer
1994 James  Investor

理想输出 #

（注：Peter无职业转换，John仅拥有两次状态，均因转换次数不足未被纳入）

From                              To
High School Teacher-Freelancer    High School Teacher
Freelancer-High School Teacher    Researcher 
Actor-Producer                    Investor

内容的提问来源于stack exchange，提问作者RandomThinker