在R中命名列表元素 [英] Naming list elements in R

问题描述

最近我一直在处理一些大型的复杂列表，并且我已经看到了一些令人惊讶的行为(至少对我来说是令人惊讶的)，主要是与为列表分配名称有关.一个简单的例子:

I've been doing some work with some large, complex lists lately and I've seen some behaviour which was surprising (to me, at least), mainly to do with assigning names to a list. A simple example:

Fil <- list(
a = list(A=seq(1, 5, 1), B=rnorm(5), C=runif(5)), 
b = list(A="Cat", B=c("Dog", "Bird"), C=list("Squirrel", "Cheetah", "Lion")),
c = list(A=rep(TRUE, 5), B=rep(FALSE, 5), C=rep(NA, 5)))

filList <- list()

for(i in 1:3){
  filList[i] <- Fil[i]
  names(filList)[i] <- names(Fil[i])
}
identical(Fil,filList)
[1] TRUE

但是:

for(i in 1:3){
  filList[i] <- Fil[i]
  names(filList[i]) <- names(Fil[i])
}
identical(Fil,filList)
[1] FALSE

我认为它使我感到困惑的主要原因是，第一个for循环中第一条names行的左侧形式需要与右侧的形式有所不同；我本以为这些应该是相同的.有人可以向我解释一下吗?

I think the main reason it confuses me is because the form of the left-hand side of first names line in the first for loop needs to be different from that of the right-hand side to work; I would have thought that these should be the same. Could anybody please explain this to me?

推荐答案

第一种情况是正确用法.在第二种情况下，您将filList[i]发送到names<-，而names<-仅作为临时子集对象存在.

The first case is the correct usage. In the second case you are sending filList[i] to names<- which is only exists as a temporary subsetted object.

或者，您可以使用以下方法完成循环外的所有操作:

Alternatively, you could just do everything outside the loop with:

names(filList) <- names(Fil)

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