Question

以下代码尝试构建一个简单的二叉树。非叶节点包含左子节点Lchild＆＃39;和一个正确的孩子＆＃39; Rchild＆＃39;叶节点不包含任何内容。这段代码的问题在于，添加变量＆root;＆＃39; root＆＃39;但是没有改变任何东西（细节参考代码中的评论）将改变＆＃39; BiTree＆＃39;的结果。代码是可执行的。结果BiTree[[2]]在调用或不调用＆＃39; root＆＃39;。

之间有所不同

## rm(list=ls()) ## ANTI-SOCIAL
set.seed(1234)

##this part generate dataset
numVar <- 40  ##number of variables
numSamples <- 400  ##number of samples
Class <- sample(c(0,1), replace = 1, numSamples)  ##categorical outcome as '0' or '1'
predictor <- matrix( sample(c(-1,0,1), replace=1, numSamples*numVar), ncol=numVar)
data <- data.frame(predictor, Class)

##BiTree is a list storing a nodes information, reprenting a tree, defined as global
BiTree <- array( list(NULL), dim = 15 )

##set i as global variable to store the ID of each node on the tree, defiend as global
i <- 1

##function to create a tree
##parameter 'root' is the ID of root node for each sub-tree
createTree <- function( data, root )
{
   ##stop grow the sub-tree if data size is smaller than 10
   if( (nrow(data) <= 10 ) )  { i <<- i + 1; return(); }

   ##seperate the data into two parts to grow left-sub-tree and right-sub-tree
   index.P1 <- 1:floor( nrow( data )/2 )
   index.P2 <- !index.P1
   data.P1 <- data[ index.P1,  ]
   data.P2 <- data[ index.P2,  ]

   ##NOTE HERE: result will differ with or without execute any of the following call of root
   ##root
   ##cat(root)
   ##print(root)

   ##i records the ID of node in the tree. it increments after one new node is added to     the tree
   i <<- i + 1

   ##record node ID for left child of the root
   BiTree[[ root ]]$Lchild <<- i

   ##create left branch
   createTree( data.P1, i )

   ##record node ID for right child of the root
   BiTree[[ root ]]$Rchild <<- i

   ##create right branch
   createTree( data.P2, i )
}

createTree( data, 1 )

##look at the second node on the tree, which will differ
(BiTree[[2]])

结果不同'没有改变任何东西'

0 个答案: