R - 替换向量列表中的元素

Question

我有一个向量列表，想将向量分配给它的一个位置(覆盖)。这是示例代码:

for (nodeId in names(chains)) {
    chains[nodeId] <- unlist(chains[nodeId])[-1]
}

分配后，我收到许多警告，告诉我列表的长度不相等。我明白已经发生的任务不是我想要的。

有什么方法可以将 chains[nodeId] 中的元素替换为对象 unlist(chains[nodeId])[-1]？

当我执行 str(chains)、str(chains[nodeId]) 和 str(unlist(chains[nodeId])[-1]) 时 我得到以下输出:

$str(chains)
List of 15
 $ 4  : chr [1:3] "root" "alcohol< 9.85" "totalSulfurDioxide>=60.5"
 $ 10 : chr [1:4] "root" "alcohol< 9.85" "totalSulfurDioxide< 60.5" "sulphates< 0.575"
 $ 22 : chr [1:5] "root" "alcohol< 9.85" "totalSulfurDioxide< 60.5" "sulphates>=0.575" ...
 (...) lots more

$str(chains[nodeId])
List of 1
 $ 4: chr [1:3] "root" "alcohol< 9.85" "totalSulfurDioxide>=60.5"

$str(unlist(chains[nodeId])[-1])
Named chr [1:2] "alcohol< 9.85" "totalSulfurDioxide>=60.5"
 - attr(*, "names")= chr [1:2] "42" "43"

更新:str替换为dput；添加了dput(chains[nodeId])

$ dput(chains)
structure(list(`4` = "alcohol< 9.85", `10` = "alcohol< 9.85", 
    `22` = "alcohol< 9.85", `92` = "alcohol< 9.85", `93` = "alcohol< 9.85", 
    `47` = "alcohol< 9.85", `24` = "alcohol>=9.85", `50` = "alcohol>=9.85", 
    `102` = "alcohol>=9.85", `103` = "alcohol>=9.85", `26` = "alcohol>=9.85", 
    `27` = "alcohol>=9.85", `28` = "alcohol>=9.85", `29` = "alcohol>=9.85", 
    `15` = c("root", "alcohol>=9.85", "alcohol>=11.55", "sulphates>=0.685"
    )), .Names = c("4", "10", "22", "92", "93", "47", "24", "50", 
"102", "103", "26", "27", "28", "29", "15"))

$ dput(chains[nodeId])
structure(list(`15` = c("root", "alcohol>=9.85", "alcohol>=11.55", 
"sulphates>=0.685")), .Names = "15")

$ dput(unlist(chains[nodeId])[-1))
structure(c("alcohol>=9.85", "alcohol>=11.55", "sulphates>=0.685"
), .Names = c("152", "153", "154"))

$ dput(chains[nodeId])
structure(list(`15` = "alcohol>=9.85"), .Names = "15")

我想要实现的是从链[nodeId]中的向量中删除第一个元素

Answer 1

如果 chains 是一个列表并且 nodeId 是一个字符串，那么 chains[nodeId] 将是一个长度为 1 的列表。您需要 chains[[nodeId]]，它包含该列表的内容。