纵向比较R…中的值

dat <- structure(list(Participant_ID = c("A", "A", "A", "A", "B", "B", 
"B", "B", "C", "C", "C", "C"), phase = structure(c(1L, 2L, 3L, 
4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L, 4L), .Label = c("base", "sixmos", 
"twelvemos", "eighteenmos"), class = "factor"), result = c("Negative", 
"Negative", "Negative", "Negative", "Negative", "Positive", "Negative", 
NA, "Positive", "Indeterminate", "Negative", "Negative")), .Names = c("Participant_ID", 
"phase", "result"), row.names = c(1L, 2L, 3L, 4L, 97L, 98L, 99L, 
100L, 9L, 10L, 11L, 12L), class = c("cast_df", "data.frame"))

看起来像:

    Participant_ID       phase        result
1                A        base      Negative
2                A      sixmos      Negative
3                A   twelvemos      Negative
4                A eighteenmos      Negative
97               B        base      Negative
98               B      sixmos      Positive
99               B   twelvemos      Negative
100              B eighteenmos          <NA>
9                C        base      Positive
10               C      sixmos Indeterminate
11               C   twelvemos      Negative
12               C eighteenmos      Negative

我想为每个测试添加一个标识符,以说明该测试是从以前的状态(从负到正)的转换,还是恢复(从正到负)或稳定。问题是,我不仅仅是比较基础测试和六个月测试,六个月到十二个月,等等-在像C这样的情况下,六个月测试应该被标记为稳定或不确定(确切的术语是不明确的),而且(更重要的是)十二个月测试应该和基础测试进行比较,并被标记为回归。相反,如果某人有一系列的“否定”、“不确定”、“否定”,那应该是稳定的。

这是后一部分,我被困在;如果只是对每个参与者进行一系列的比较,我会没事的,但我在思考如何优雅地处理这些可变的比较对时遇到了困难。一如既往,我们非常感谢你的帮助。