r - R 中的特定排序

Question

我正在为特定输入进行所有可能的组合，但它也必须根据输入的顺序进行排序。由于组合的大小不同，我正在为之前发布的答案而苦苦挣扎。

我想知道这是否可能。

输入:

D N A 3

这意味着我需要在最多 3 个字符串的所有组合中输出它:

D
DD
DDD
DDN
DDA
DND
DNA
. 
.

如果我们考虑 D<N<A，这基本上是升序

到目前为止，我的输出如下所示:

A
AA
AAA
AAD
AAN
AD
ADA
ADD
ADN
AN
.
.

我尝试将输入转换为因子 c("D","N","A")并对我的输出进行排序，但随后它会消失任何大于 1 个字符的字符串。

Answer 1

这是一种可能的解决方案:

generateCombs <- function(x, n){
  if (n == 1) return(x[1]) # Base case
  # Create a grid with all possible permutations of 0:n. 0 == "", and 1:n correspond to elements of x
  permutations = expand.grid(replicate(n, 0:n, simplify = F)) 
  # Order permutations
  orderedPermutations = permutations[do.call(order, as.list(permutations)),] 
  # Map permutations now such that 0 == "", and 1:n correspond to elements of x
    mappedPermutations = sapply(orderedPermutations, function(y) c("", x)[y + 1])
  # Collapse each row into a single string
  collapsedPermutations = apply(mappedPermutations, 1, function(x) paste0(x, collapse = ""))
  # Due to the 0's, there will be duplicates. We remove the duplicates in reverse order
  collapsedPermutations = rev(unique(rev(collapsedPermutations)))[-1] # -1 removes blank
  # Return as data frame
  return (as.data.frame(collapsedPermutations))
}

x = c("D", "N", "A")
n = 3
generateCombs(x, n)

输出是:

   collapsedPermutations
1                      D
2                     DD
3                    DDD
4                    DDN
5                    DDA
6                     DN
7                    DND
8                    DNN
9                    DNA
10                    DA
11                   DAD
...