从 ctree 对象中提取预测变量

Posted 2023-03-12

【中文标题】从 ctree 对象中提取预测变量

【英文标题】：extracting predictors from ctree object

【发布时间】：2013-07-16 19:15:10

【问题描述】：

我检查了 binary tree 类方法和 How to extract tree structure from ctree function?（这有助于理解 S4 对象结构和插槽），但仍不清楚如何获得 ctree 对象的最终预测变量。对于rpart，我会使用类似

 extract_preds <- function( tt )
   leaves <- tt$frame$var == '<leaf>'
   as.character( unique( tt$frame$var[ leaves==F ] ) )
 

是否有类似的快捷方式可用，还是我必须编写一个递归函数来遍历ctree 对象并提取预测变量？那，还是带有打印输出的正则表达式？谢谢。

更新：使用 baydoganm 的代码如下。仍然需要弄清楚如何通过递归正确更新res：

 library(party)

 ctree_preds <- function(tr,vnames)    
    res <- character(0)
    traverse <- function(treenode,vnames,res)
    if(treenode$terminal)
        return(res)
     else 
        res <- c(res,vnames[treenode$psplit$variableID])
        traverse(treenode$left , vnames, res )
        traverse(treenode$right, vnames, res )
        
    
    traverse(tr,vnames,res)
    return(unique(res))
 

 airq <- subset(airquality, !is.na(Ozone))
 airct <- ctree(Ozone ~ ., data = airq,
                         controls = ctree_control(maxsurrogate = 3))
 plot(airct)

 ctree_preds(airct@tree,names(airq)[-1])

【问题讨论】：

你必须遍历树。

【参考方案1】：

下面是我实现的从ctree 对象遍历树的脚本。我在party 包中使用相同的示例，即airct 数据集。

require(party)
data(airquality)

traverse <- function(treenode)
    if(treenode$terminal)
        bas=paste("Current node is terminal node with",treenode$nodeID,'prediction',treenode$prediction)
        print(bas)
        return(0)
     else 
        bas=paste("Current node",treenode$nodeID,"Split var. ID:",treenode$psplit$variableName,"split value:",treenode$psplit$splitpoint,'prediction',treenode$prediction)
        print(bas)

traverse(treenode$left)
traverse(treenode$right)


airq <- subset(airquality, !is.na(Ozone))
airct <- ctree(Ozone ~ ., data = airq,
controls = ctree_control(maxsurrogate = 3))
plot(airct)

traverse(airct@tree)

这个函数，traverse，只是以深度优先的顺序遍历树。可以通过改变递归部分来改变遍历的顺序。

另外，如果要返回其他节点特征，我建议检查 ctree 对象的结构。

编辑：次要代码修订。

【讨论】：

我已经运行了上面的代码并且节点varriableID 没有打印出来。由于目标是获得一个带有预测变量名称的向量，因此我正在使用您的代码来解决这个问题（请参阅问题）。我正在苦苦挣扎的是如何以类似于 C 的地址运算符的方式通过递归更新res。

我不确定您是否使用相同的派对包，但上面的代码对我有用。如果您有兴趣打印变量的名称，只需将treenode$psplit$variableID 更改为treenode$psplit$variableName。但是，我不确定这是否是您要问的。我还稍微更新了代码。

我使用函数capture.output将值存储在data.frame中以供进一步处理

【参考方案2】：

mlmeta R 包的 ctree2sas() 函数将拟合的 ctree 模型转换为 SAS 代码。它可以很容易地适应其他语言，并且通常对对象的内部具有指导意义。

【参考方案3】：

split <- 
c(cart@tree$psplit$splitpoint , cart@tree$right$psplit$splitpoint , cart@tree$left$psplit$splitpoint , cart@tree$right$right$psplit$splitpoint , cart@tree$right$left$psplit$splitpoint , cart@tree$left$right$psplit$splitpoint , cart@tree$left$left$psplit$splitpoint , cart@tree$right$right$right$psplit$splitpoint , cart@tree$right$right$left$psplit$splitpoint , cart@tree$right$left$right$psplit$splitpoint , cart@tree$right$left$left$psplit$splitpoint , cart@tree$left$right$right$psplit$splitpoint , cart@tree$left$right$left$psplit$splitpoint , cart@tree$left$left$right$psplit$splitpoint , cart@tree$left$left$left$psplit$splitpoint , cart@tree$right$right$right$right$psplit$splitpoint , cart@tree$right$right$right$left$psplit$splitpoint , cart@tree$right$right$left$right$psplit$splitpoint , cart@tree$right$right$left$left$psplit$splitpoint , cart@tree$right$left$right$right$psplit$splitpoint , cart@tree$right$left$right$left$psplit$splitpoint , cart@tree$right$left$left$right$psplit$splitpoint , cart@tree$right$left$left$left$psplit$splitpoint , cart@tree$left$right$right$right$psplit$splitpoint , cart@tree$left$right$right$left$psplit$splitpoint , cart@tree$left$right$left$right$psplit$splitpoint , cart@tree$left$right$left$left$psplit$splitpoint , cart@tree$left$left$right$right$psplit$splitpoint , cart@tree$left$left$right$left$psplit$splitpoint , cart@tree$left$left$left$right$psplit$splitpoint , cart@tree$left$left$left$left$psplit$splitpoint , cart@tree$left$left$left$left$left$psplit$splitpoint , cart@tree$left$left$left$left$right$psplit$splitpoint , cart@tree$left$left$left$right$left$psplit$splitpoint , cart@tree$left$left$left$right$right$psplit$splitpoint , cart@tree$left$left$right$left$left$psplit$splitpoint , cart@tree$left$left$right$left$right$psplit$splitpoint , cart@tree$left$left$right$right$left$psplit$splitpoint , cart@tree$left$left$right$right$right$psplit$splitpoint , cart@tree$left$right$left$left$left$psplit$splitpoint , cart@tree$left$right$left$left$right$psplit$splitpoint , cart@tree$left$right$left$right$left$psplit$splitpoint , cart@tree$left$right$left$right$right$psplit$splitpoint , cart@tree$left$right$right$left$left$psplit$splitpoint , cart@tree$left$right$right$left$right$psplit$splitpoint , cart@tree$left$right$right$right$left$psplit$splitpoint , cart@tree$left$right$right$right$right$psplit$splitpoint , cart@tree$right$left$left$left$left$psplit$splitpoint , cart@tree$right$left$left$left$right$psplit$splitpoint , cart@tree$right$left$left$right$left$psplit$splitpoint , cart@tree$right$left$left$right$right$psplit$splitpoint , cart@tree$right$left$right$left$left$psplit$splitpoint , cart@tree$right$left$right$left$right$psplit$splitpoint , cart@tree$right$left$right$right$left$psplit$splitpoint , cart@tree$right$left$right$right$right$psplit$splitpoint , cart@tree$right$right$left$left$left$psplit$splitpoint , cart@tree$right$right$left$left$right$psplit$splitpoint , cart@tree$right$right$left$right$left$psplit$splitpoint , cart@tree$right$right$left$right$right$psplit$splitpoint , cart@tree$right$right$right$left$left$psplit$splitpoint , cart@tree$right$right$right$left$right$psplit$splitpoint , cart@tree$right$right$right$right$left$psplit$splitpoint , cart@tree$right$right$right$right$right$psplit$splitpoint)

split <- split[order(split)]