在嵌套列表中找到元素的索引? [英] Find the indices of an element in a nested list?

问题描述

我有一个类似的列表:

mylist <- list(a = 1, b = list(A = 1, B = 2), c = list(C = 1, D = 3))

是否有(无环)标识元素位置的方法，例如如果我想将"C"的值替换为5，并且无论在哪里找到"C"元素，我都可以执行以下操作:

is there an (loop-free) way to identify the positions of the elements, e.g. if I want to replace a values of "C" with 5, and it does not matter where the element "C" is found, can I do something like:

Aindex <- find_index("A", mylist)
mylist[Aindex] <- 5

我已经尝试过grepl，在当前示例中，以下方法将起作用:

I have tried grepl, and in the current example, the following will work:

mylist[grepl("C", mylist)][[1]][["C"]]

但这需要假设嵌套级别.

but this requires an assumption of the nesting level.

我问的原因是我有一个很深的参数值列表，以及一个替换值的命名向量，我想做类似的事情

The reason that I ask is that I have a deep list of parameter values, and a named vector of replacement values, and I want to do something like

 replacements <- c(a = 1, C = 5)
 for(i in names(replacements)){ 
    indx <- find_index(i, mylist)
    mylist[indx] <-  replacements[i]
  }

这是我以前的问题的改编，使用R中的xpath更新(未知深度)节点，，使用R列表而不是XML

this is an adaptation to my previous question, update a node (of unknown depth) using xpath in R?, using R lists instead of XML

推荐答案

一种方法是使用unlist和relist.

mylist <- list(a = 1, b = list(A = 1, B = 2), c = list(C = 1, D = 3))
tmp <- as.relistable(mylist)
tmp <- unlist(tmp)
tmp[grep("(^|.)C$",names(tmp))] <- 5
tmp <- relist(tmp)

由于unlist中的列表名称与.串联在一起，因此在使用grep以及如何命名参数时要格外小心.如果您的任何列表名称中都没有.，应该没问题.否则，list(.C = 1)之类的名称将落入该模式并被替换.

Because list names from unlist are concatenated with a ., you'll need to be careful with grep and how your parameters are named. If there is not a . in any of your list names, this should be fine. Otherwise, names like list(.C = 1) will fall into the pattern and be replaced.

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