使用“...”和“复制”

发布于 11-24 16:40 字数 935 浏览 2 评论 0原文

sapplyreplicate 的文档中,有一个关于使用 ... 的警告

,现在,我可以接受它,但想了解其背后的内容。所以我创建了这个小例子:

innerfunction<-function(x, extrapar1=0, extrapar2=extrapar1)
{
    cat("x:", x, ", xp1:", extrapar1, ", xp2:", extrapar2, "\n")
}

middlefunction<-function(x,...)
{
    innerfunction(x,...)
}

outerfunction<-function(x, ...)
{
    cat("Run middle function:\n")
    replicate(2, middlefunction(x,...))
    cat("Run inner function:\n")
    replicate(2, innerfunction(x,...))
}

outerfunction(1,2,3)
outerfunction(1,extrapar1=2,3)
outerfunction(1,extrapar1=2,extrapar2=3)

也许我做了一些明显错误的事情,但我发现这个结果相当令人沮丧。那么任何人都可以向我解释为什么在上述所有对 outerfunction 的调用中,我得到这个输出:

Run middle function:
x: 1 , xp1: 0 , xp2: 0 
x: 1 , xp1: 0 , xp2: 0 
Run inner function:
x: 1 , xp1: 0 , xp2: 0 
x: 1 , xp1: 0 , xp2: 0

就像我说的:文档似乎对此发出警告,但我不明白为什么会这样。

In the documentation of sapply and replicate there is a warning regarding using ...

Now, I can accept it as such, but would like to understand what is behind it. So I've created this little contrived example:

innerfunction<-function(x, extrapar1=0, extrapar2=extrapar1)
{
    cat("x:", x, ", xp1:", extrapar1, ", xp2:", extrapar2, "\n")
}

middlefunction<-function(x,...)
{
    innerfunction(x,...)
}

outerfunction<-function(x, ...)
{
    cat("Run middle function:\n")
    replicate(2, middlefunction(x,...))
    cat("Run inner function:\n")
    replicate(2, innerfunction(x,...))
}

outerfunction(1,2,3)
outerfunction(1,extrapar1=2,3)
outerfunction(1,extrapar1=2,extrapar2=3)

Perhaps I've done something obvious horribly wrong, but I find the result of this rather upsetting. So can anyone explain to me why, in all of the above calls to outerfunction, I get this output:

Run middle function:
x: 1 , xp1: 0 , xp2: 0 
x: 1 , xp1: 0 , xp2: 0 
Run inner function:
x: 1 , xp1: 0 , xp2: 0 
x: 1 , xp1: 0 , xp2: 0

Like I said: the docs seem to warn for this, but I do not see why this is so.

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评论(4

·深蓝2024-12-01 16:40:38

示例部分中的 ?replicate 明确告诉我们您尝试做的事情不会也不会起作用。在 ?replicateNote 部分中,我们有:

     If ‘expr’ is a function call, be aware of assumptions about where
     it is evaluated, and in particular what ‘...’ might refer to.  You
     can pass additional named arguments to a function call as
     additional named arguments to ‘replicate’: see ‘Examples’.

如果我们查看示例,我们会看到:

 ## use of replicate() with parameters:
 foo <- function(x=1, y=2) c(x,y)
 # does not work: bar <- function(n, ...) replicate(n, foo(...))
 bar <- function(n, x) replicate(n, foo(x=x))
 bar(5, x=3)

我对文档的阅读是,它们的作用远不止警告您使用...replicate() 调用中;他们明确证明它不起作用。该帮助文件中的大部分讨论都与其他函数的...参数有关,不一定与replicate()有关。

?replicate, in the Examples section, tells us explicitly that what you are trying to do does not and will not work. In the Note section of ?replicate we have:

     If ‘expr’ is a function call, be aware of assumptions about where
     it is evaluated, and in particular what ‘...’ might refer to.  You
     can pass additional named arguments to a function call as
     additional named arguments to ‘replicate’: see ‘Examples’.

And if we look at Examples, we see:

 ## use of replicate() with parameters:
 foo <- function(x=1, y=2) c(x,y)
 # does not work: bar <- function(n, ...) replicate(n, foo(...))
 bar <- function(n, x) replicate(n, foo(x=x))
 bar(5, x=3)

My reading of the docs is that they do far more than warn you about using ... in replicate() calls; they explicitly document that it does not work. Much of the discussion in that help file relates to the ... argument of the other functions, not necessarily to replicate().

鹿港小镇2024-12-01 16:40:38

如果您查看 replicate 的代码:

> replicate
function (n, expr, simplify = TRUE) 
sapply(integer(n), eval.parent(substitute(function(...) expr)), 
    simplify = simplify)
<environment: namespace:base>

您会看到该函数在父框架中求值,其中调用函数的 ... 不再存在。

If you look at the code for replicate:

> replicate
function (n, expr, simplify = TRUE) 
sapply(integer(n), eval.parent(substitute(function(...) expr)), 
    simplify = simplify)
<environment: namespace:base>

You see that the function is evaluated in the parent frame, where the ... from your calling function no longer exists.

木格2024-12-01 16:40:38

实际上有一种方法可以做到这一点:

# Simple function:
ff <- function(a,b) print(a+b)

# This will NOT work:
testf <- function(...) {
  replicate(expr = ff(...), n = 5)
}
testf(45,56) # argument "b" is missing, with no default

# This will:
testf <- function(...) {
  args <- as.list(substitute(list(...)))[-1L]
  replicate(expr = do.call(ff, args), n = 5)
}
testf(45,56) # 101

There actually is a way to do this:

# Simple function:
ff <- function(a,b) print(a+b)

# This will NOT work:
testf <- function(...) {
  replicate(expr = ff(...), n = 5)
}
testf(45,56) # argument "b" is missing, with no default

# This will:
testf <- function(...) {
  args <- as.list(substitute(list(...)))[-1L]
  replicate(expr = do.call(ff, args), n = 5)
}
testf(45,56) # 101
瘫痪情歌2024-12-01 16:40:38

另一种方法是:

g <- function(x, y) x + y

f <- function(a = 1, ...) {
    arg_list <- list(...)
    replicate(n = 3, expr = do.call(g, args = arg_list))
}

f(x = 1, y = 2)

An alternative way to do that:

g <- function(x, y) x + y

f <- function(a = 1, ...) {
    arg_list <- list(...)
    replicate(n = 3, expr = do.call(g, args = arg_list))
}

f(x = 1, y = 2)
~没有更多了~
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