r - lapply - 环境中存在命名参数时传递和不传递参数的区别

Question

请参阅最后的编辑以获取可重现的示例。

问题描述

当我boot::censboot(data, statistic, parallel = "multicore", ncpus = 2, var = whatEver)在我定义的地方运行时，statistic <- function(data, var)我收到类型的错误消息FUN(X[[i]], ...) : unused argument (var = whatEver)。问题是statistic无法看到var.

我打电话时不会发生这种情况boot::censboot(data, statistic, parallel = "no")。

通过调试我可以看到：

• 如果parallel = "no",boot::censboot正在运行这样的事情：

  stat <- function(r, s){r + s}
  
  main <- function(...)
  {
    fn <- {function(r) stat(r, ...)}
    lapply(1:2, fn)
  }
  
  main(s = 2)
  

  输出：

  [[1]]
  [1] 3
  
  [[2]]
  [1] 4
  

  在这种情况下stat确实能够看到s = 1，即使fn只是r（而不是rAND ...）的函数。

• 但是如果parallel = "multicore", ncpus = 2, thenboot::censboot运行类似这样的东西（请注意，与上述代码块的唯一区别在于...）lapply：

  stat <- function(r, s){r + s}
  
  main <- function(...)
  {
     fn <- {function(r) stat(r, ...)}
     lapply(1:2, fn, ...)
  }
  
  main(s = 2)
  

  输出：

  Error in FUN(X[[i]], ...) : unused argument (s = 2)
  

  在这种情况下stat是看不到的s = 1。这是未使用参数类型的错误消息的根本原因。

  （当然，实际上是调用boot::censboot而parallel::mclapply不是lapply并行化，但问题与.......lapplyparallel::mclapplyboot::censboot

问题：

1. 为什么会这样？在普通情况下，如何stat才能看到实际不使用传递参数的地方？为什么在并行情况下使用时这不再正确？s = 1lapply...lapply...
2. 我无法更改 的内部结构main，它表示在boot::censboot. 我该如何更改stat以使其在两种情况下都有效？

编辑：添加了可重现的示例

根据下面评论者的要求，这是一个在并行情况下重现错误的示例。如果您parallel = "no", ncpus = 1在boot::censboot代码中设置按预期工作。

library(boot)
library(survival)
data(aml, package = "boot") 

statMeanSurv <- function(data, var) {
  surv <- survfit(Surv(time, cens) ~ 1, data = data)
  mean(surv$surv) + var
}

res <- censboot(aml, statMeanSurv, R = 5,
                var = 1, parallel = "multicore", ncpus = 2)

res$t

输出：

> res <- censboot(aml, statMeanSurv, R = 5,
+                 var = 1, parallel = "multicore", ncpus = 2)
Warning message:
In parallel::mclapply(seq_len(R), fn, ..., mc.cores = ncpus) :
  all scheduled cores encountered errors in user code
> 
> res$t
     [,1]                                                     
[1,] "Error in FUN(X[[i]], ...) : unused argument (var = 1)\n"
[2,] "Error in FUN(X[[i]], ...) : unused argument (var = 1)\n"
[3,] "Error in FUN(X[[i]], ...) : unused argument (var = 1)\n"
[4,] "Error in FUN(X[[i]], ...) : unused argument (var = 1)\n"
[5,] "Error in FUN(X[[i]], ...) : unused argument (var = 1)\n"

标签： r

Answer 1

This is a rewrite of the original post, that gives a better explanation of what went wrong, and fixes a possible bug in the workaround.

That looks like a bug in censboot. It doesn't handle the ... parameter correctly. (More explanation below.) The reason you don't get an error with parallel = 'no' is that the code follows a different path.

A workaround is to use "partial application" to create a 1-parameter statistic function, like this:

library(boot)
library(survival)
#> 
#> Attaching package: 'survival'
#> The following object is masked from 'package:boot':
#> 
#>     aml
data(aml, package = "boot") 

statMeanSurv <- function(data, var) {
  surv <- survfit(Surv(time, cens) ~ 1, data = data)
  mean(surv$surv) + var
}

statMeanSurv1 <- function(var) { 
  force(var)   # Fix the value of var
  function(mean) statMeanSurv(mean, var) 
}

res <- censboot(aml, statMeanSurv1(var = 1), R = 5,
                parallel = "multicore", ncpus = 2)

res$t
#>          [,1]
#> [1,] 1.564580
#> [2,] 1.503473
#> [3,] 1.602111
#> [4,] 1.440942
#> [5,] 1.594482

^{Created on 2021-02-04 by the reprex package (v0.3.0)}

Internally, the problem in censboot is that it does something like my workaround, but then it also passes ... to its equivalent of statMeanSurv1, and that's an error: it can only accept 1 argument.

The line force(var) in statMeanSurv1 isn't necessary in the example, but in more elaborate examples it might be. It guarantees that the newly created function uses the specified value.