如何在 R 环境中使用变量的值作为键? [英] How to use the value of a variable as key in an R-environment?

问题描述

在 R 编程语言中，我想使用哈希表.

In R programming language I want to use a hash table.

如何使用变量的值作为环境的键?

How do I use the value of a variable as the key for the environment?

例如:

map <- new.env(hash=T, parent=emptyenv())
key <- 'ddd'
map$key <- 4
print(ls(map))
>>[1] "key"

输出是'key'，这意味着我得到了从字符串'key'到值4的映射.我真正想要这段代码做的是将字符串'ddd'映射到值4.

The output is 'key', which means I get a mapping from the string 'key' to the value 4. What I really want this code to do is to map the string 'ddd' to the value 4.

我怎样才能做到这一点?

How can I achieve this?

PS.我不使用命名列表，因为它不使用散列来进行搜索，因为它对大量元素很慢.

PS. I don't use named list because it's slow with large amount of elements as it does not use hashing to do the search.

推荐答案

正如 ?"$" 中所说:

 Both ‘[[’ and ‘$’ select a single element of the list.  The main
 difference is that ‘$’ does not allow computed indices, whereas
 ‘[[’ does.  ‘x$name’ is equivalent to ‘x[["name", exact =
 FALSE]]’.  Also, the partial matching behavior of ‘[[’ can be
 controlled using the ‘exact’ argument.

所以你想要:

map[[key]] <- 4
> print(ls(map))
[1] "ddd" "key"
> map[[key]]
[1] 4

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