如何对排列“进行中"进行检查.而不将结果存储在R中 [英] How to perform a check on a permutation "on-the-fly" without storing the result in R

问题描述

假设我们对字母"a"，"b"和"c"进行以下排列:

Assume we have the following permutations of the letters, "a", "b", and "c":

library(combinat)
do.call(rbind, permn(letters[1:3]))
#      [,1] [,2] [,3]
# [1,] "a"  "b"  "c" 
# [2,] "a"  "c"  "b" 
# [3,] "c"  "a"  "b" 
# [4,] "c"  "b"  "a" 
# [5,] "b"  "c"  "a" 
# [6,] "b"  "a"  "c" 

是否可以在给定的即时"排列(即特定行)上执行某些功能而无需存储结果?

Is it possible to perform some function on a given permutation "on-the-fly" (i.e., a particular row) without storing the result?

也就是说，如果row == "a" "c" "b"或row == "b" "c" "a"，则不存储结果.在这种情况下，理想的结果将是:

That is, if the row == "a" "c" "b" or row == "b" "c" "a", do not store the result. The desired result in this case would be:

#      [,1] [,2] [,3]
# [1,] "a"  "b"  "c" 
# [2,] "c"  "a"  "b" 
# [3,] "c"  "b"  "a" 
# [4,] "b"  "a"  "c" 

我知道我可以使用fun参数将函数应用到combinat::permn中的所有动态排列中，例如:

I know I can apply a function to all the permutations on the fly within combinat::permn with the fun argument such as:

permn(letters[1:3], fun = function(x) {
  res <- paste0(x, collapse = "")
  if (res == "acb" | res == "bca") {
    return(NA)
  } else {
    return(res)
  }
})

但这仍然存储一个NA，并且返回的列表包含6个元素，而不是所需的4个元素:

But this stills stores an NA and the returned list has 6 elements instead of the desired 4 elements:

# [[1]]
# [1] "abc"
# 
# [[2]]
# [1] NA
# 
# [[3]]
# [1] "cab"
# 
# [[4]]
# [1] "cba"
# 
# [[5]]
# [1] NA
# 
# [[6]]
# [1] "bac"

注意，我对随后删除NA值不感兴趣；我特别感兴趣的是，不对给定的排列即时"添加到结果列表中.

Note, I am not interested in subsequently removing the NA values; I am specifically interested in not appending to the result list "on-the-fly" for a given permutation.

推荐答案

我们可以使用magrittr管道，在该管道中，将输入矩阵绑定到要检查的行，并省略重复的行.

We could use a magrittr pipeline where we rbind the input matrix to the Rows to be checked and omit the duplicate rows.

library(combinat)
library(magrittr)

Rows <- rbind(c("a", "c", "b"), c("b", "c", "a"))

do.call(rbind, permn(letters[1:3])) %>% 
  subset(tail(!duplicated(rbind(Rows, .)), -nrow(Rows)))

给予:

     [,1] [,2] [,3]
[1,] "a"  "b"  "c" 
[2,] "c"  "a"  "b" 
[3,] "c"  "b"  "a" 
[4,] "b"  "a"  "c" 

这篇关于如何对排列“进行中"进行检查.而不将结果存储在R中的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！