R中列表元素的排列

Question

我正在尝试获取部分列表元素的排列。我可以用

得到规则的排列

my_list <- list('A' = c("A"), 'B'= c('B', 'B'), "C" = c('C', "C", "C"))
combinat::permn(my_list)

但是，我只需要 3 个可能的元素中的 2 个，例如combinat::permn(my_list)[[1]][1:2] 将是期望的结果之一

combinat::permn(my_list)[[1]][1:2]
$A
[1] "A"

$B
[1] "B" "B"

combinat::permn 不允许这些 'partial' 排列。获得部分排列的好方法是什么？

Answer 1

我们可以使用combn

combn(my_list, 2, simplify = FALSE)

-输出

[[1]]
[[1]]$A
[1] "A"

[[1]]$B
[1] "B" "B"


[[2]]
[[2]]$A
[1] "A"

[[2]]$C
[1] "C" "C" "C"


[[3]]
[[3]]$B
[1] "B" "B"

[[3]]$C
[1] "C" "C" "C"

Answer 2

您将需要使用能够生成长度排列的包之一 n 一次选择 m（参见此 How to generate permutations or combinations of object in R? 了解更多信息）。然后，您可以遍历行并对原始列表进行子集化：

library(gtools)

apply(permutations(length(my_list), 2), 1, function(x) {
    my_list[x]
})

[[1]]
[[1]]$A
[1] "A"

[[1]]$B
[1] "B" "B"


[[2]]
[[2]]$A
[1] "A"

[[2]]$C
[1] "C" "C" "C"


[[3]]
[[3]]$B
[1] "B" "B"

[[3]]$A
[1] "A"


[[4]]
[[4]]$B
[1] "B" "B"

[[4]]$C
[1] "C" "C" "C"


[[5]]
[[5]]$C
[1] "C" "C" "C"

[[5]]$A
[1] "A"


[[6]]
[[6]]$C
[1] "C" "C" "C"

[[6]]$B
[1] "B" "B"

R中列表元素的排列

Permutations of list elements in R

r

permutation