PST 何时从左到右和从右到左显示上下文？答案

【问题标题】：When does PST display contexts from left to right and right to left?PST 何时从左到右和从右到左显示上下文？
【发布时间】：2017-03-03 16:22:09
【问题描述】：

PST 包是否总是从右到左显示上下文？

在query() 函数中，我们使用字符串来表示上下文。如果我假设上下文是从右到左指定的（因为它似乎在 print() 和 cmine() 函数中），并且我对序列 A->B->C 感兴趣，那么我应该查询：

query(S1.p1, "C-B-A")

此外，在predict() 函数中，我们使用seqdef() 来定义要预测的序列。这是否意味着我应该像 TraMineR 通常那样从左到右指定它们？

x <- seqdef("A-B-C)
predict(S1.p1, x)

【问题讨论】：

标签： r pst traminer

【解决方案1】：

在概率后缀树 (PST) 中，当我们从根开始读取分支时，它会从右到左定义一个后缀。在第一层，您有后缀的最后一个元素，在第 2 层，您有最后一个元素之前的元素，依此类推。打印的树在左侧显示根，并从左到右展开。尽管如此，打印结果的节点中显示的后缀应该自然地从左到右阅读。例如，节点a-b-c 表示以c 结尾的后缀。这样一个节点是从节点b-c左边加上a得到的。

cmine 的结果也是如此。对于每个找到的上下文，例如a-b-c, cmine 给出了在上下文之后立即获得每个可能状态的概率，即示例中的c 之后。

总之，序列和上下文总是从左到右显示，即使上下文是从右到左构建的。

所以，如果您想查询序列A->B->C，只需使用query(S1.p1, "A-B-C")。同样，要使用predict 预测特定序列，请自然地从左到右定义序列。

【讨论】：

【解决方案2】：

序列应该从左到右阅读。以下代码对此进行了验证：

library(PST)
data.seq <- seqdef("A-B-C-D-E-F")
S1.test <- pstree(data.seq, ymin = 0.001, lik = FALSE, with.missing = FALSE)
print(S1.test)

--(e)-[ p=(0.2,0.2,0.2,0.2,0.2,0.2) - n=6 ]
  `--(A)-[ p=(0.001,0.995,0.001,0.001,0.001,0.001) - n=1 ]--| 
  `--(B)-[ p=(0.001,0.001,0.995,0.001,0.001,0.001) - n=1 ]
     `--(A-B)-[ p=(0.001,0.001,0.995,0.001,0.001,0.001) - n=1 ]--| 
  `--(C)-[ p=(0.001,0.001,0.001,0.995,0.001,0.001) - n=1 ]
     `--(B-C)-[ p=(0.001,0.001,0.001,0.995,0.001,0.001) - n=1 ]
        `--(A-B-C)-[ p=(0.001,0.001,0.001,0.995,0.001,0.001) - n=1 ]--| 
  `--(D)-[ p=(0.001,0.001,0.001,0.001,0.995,0.001) - n=1 ]
     `--(C-D)-[ p=(0.001,0.001,0.001,0.001,0.995,0.001) - n=1 ]
        `--(B-C-D)-[ p=(0.001,0.001,0.001,0.001,0.995,0.001) - n=1 ]
           `--(A-B-C-D)-[ p=(0.001,0.001,0.001,0.001,0.995,0.001) - n=1 ]--| 
  `--(E)-[ p=(0.001,0.001,0.001,0.001,0.001,0.995) - n=1 ]
     `--(D-E)-[ p=(0.001,0.001,0.001,0.001,0.001,0.995) - n=1 ]
        `--(C-D-E)-[ p=(0.001,0.001,0.001,0.001,0.001,0.995) - n=1 ]
           `--(B-C-D-E)-[ p=(0.001,0.001,0.001,0.001,0.001,0.995) - n=1 ]
              `--(A-B-C-D-E)-[ p=(0.001,0.001,0.001,0.001,0.001,0.995) - n=1 ]--|


plot(S1.test)

这也表明绘制的树应该从下到上阅读。

【讨论】：