英文:
Create S4 slots dynamically
问题
I can provide you with a translation of the code part you've provided:
我想动态创建（或扩展）已定义的S4类的插槽，其中插槽名称和类型存储在一个变量中。
手动的方法如下：
```R
setClass("ClassA", representation(
Slot1 = "character",
Slot2 = "numeric",
Slot3 = "character"
))
但我想从一个变量中检索插槽名称和类型：
slotName <- list("slot1", "slot2", "slot3")
slotType <- list("character", "numeric", "character")
slots <- map2(slotName, slotType, ~ str_c(.x, "=", '"', .y, '"'))
我该如何使用非标准评估（NSE）来创建类？
我尝试使用eval(parse_expr())来引用类定义内部的表达式：
y <- str_c(slotName[1], "=", '"', slotType[1], '"')
setClass("classA", representation(
eval(parse_expr(y))
))
x <- new("classA")
但这里对象x的结构是：
> str(x)
Formal class 'classA' [.GlobalEnv] with 1 slot
..@ .Data: chr(0)
不幸的是，没有slot1。在类定义中映射向量也不起作用。
Please note that the translation retains the code structure and formatting. If you have any questions or need further assistance, please feel free to ask.
<details>
<summary>英文:</summary>
I would like to create (or extend) slots of a defined S4 class dynamically, where slots names and types are stored in a variable.
A manual approach would be:
setClass("ClassA", representation(
Slot1 = "character",
Slot2 = "numeric",
Slot3 = "character"
))
But I would like to retrieve slot names and types from a variable:
slotName <- list("slot1", "slot2", "slot3")
slotType <- list("character", "numeric", "character")
slots <- map2(slotName, slotType, ~ str_c(.x, "=", '"', .y, '"'))
How can I create the class with NSE?
I tried with `eval(parse_expr())` to quote the expression within the class definition:
y <- str_c(slotName[1], "=", '"', slotType[1], '"')
setClass("classA", representation(
eval(parse_expr(y))
))
x <- new("classA")
But here the structure of the object `x` is:
> str(x)
Formal class 'classA' [package ".GlobalEnv"] with 1 slot
..@ .Data: chr(0)`
with no `slot1`, unfortunately. Mapping vectors in the class definition did not work either.
</details>
# 答案1
**得分**: 4
在需要设置参数名称时，更好的策略是构建一个具有命名列表，并使用 `do.call` 来运行一个函数。最好避免使用 `eval()`；通常有更好的选项。在这种情况下，你可以这样做：
```R
setClass("ClassA",
do.call("representation", setNames(slotType, slotName))
)
x <- new("ClassA")
str(x)
# Formal class 'ClassA' [package ".GlobalEnv"] with 3 slots
# ..@ slot1: chr(0)
# ..@ slot2: num(0)
# ..@ slot3: chr(0)
英文:
When you need to set names of parameters, the better strategy is to build a named list and use do.call to run a function. It's best to avoid eval(); there are almost always better options. In this case you can do
setClass("ClassA",
do.call("representation", setNames(slotType, slotName))
)
x <- new("ClassA")
str(x)
# Formal class 'ClassA' [package ".GlobalEnv"] with 3 slots
# ..@ slot1: chr(0)
# ..@ slot2: num(0)
# ..@ slot3: chr(0)
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