转换为循环应用 [英] Convert for loop to apply

问题描述

在 R 中，如何使用 apply、lapply、rapply、do.call<等函数替换以下代码/code> 等?

In R, how do you replace the following code using functions like apply, lapply, rapply, do.call, etc.?

u <- 10:12
slist <- list()

for (i in 1:length(u)) {
  p <- combn(u, i) 
  for (j in 1:ncol(p)) {
    s <- paste(p[,j], collapse=",")
    slist[[s]] <- 0
  }
}

对于这部分:

  for (j in 1:ncol(p)) {
    s <- paste(p[,j], collapse=",")

我尝试了类似的东西:

  s <- apply(p, 2, function(x) paste(x, collapse=","))

哪个有效.但是对于同一 for 循环中的 slist[[s]] <- 0 部分，我不知道该怎么做.

Which works. But then for that slist[[s]] <- 0 part inside that same for-loop, I don't know what to do.

这就是我想要做的.对于向量 u，我正在生成该向量中所有子集的列表.然后对于每个子集，我将其分配给 s，然后使用字符串 s 作为 slist 中元素的名称.有点奇怪，我知道，但这是家庭作业.对于上面的代码，这将是 slist 的前 5 个元素:

This is what I'm trying to do. For the vector u, I'm producing a list of all the subsets in that vector. Then for each subset, I'm assigning it to s, then using the string s as the name of an element in slist. Kind of strange, I know, but it's for a homework assignment. For the code above, this would be the first 5 elements of slist:

 > slist
 $`10`
 [1] 0

 $`11`
 [1] 0

 $`12`
 [1] 0

 $`10,11`
 [1] 0

 $`10,12`
 [1] 0

是的，我只是想学习如何正确使用 apply 和 stuff.

Yeah, I'm just trying to learn how to use apply and stuff properly.

推荐答案

这是一个解决方案:

n <- unlist(lapply(seq_along(u), function(i) {
  apply(combn(length(u),i),2, function(x) paste(u[x], collapse=','))
}
))

slist <- list()
slist[n] <- 0

UPDATE 与@djhurio 同时发布，非常相似，但我冒昧更改了combn 的使用，以便处理u 长度为 1，正如@djhurio 指出的那样.

UPDATE Posted at the same time as @djhurio, it is very similar, but I took the liberty of changing the use of combn so it handles u of length 1, as @djhurio pointed out.

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