R找到所有可能的独特组合 [英] R find all possible unique combinations

问题描述

我正在尝试在R中找到所有可能的唯一组合.似乎有很多类似的问题要问，但是我找不到相同的问题.

I am trying to find all possible unique combinations in R. It seems that there have been a lot of similar questions asked, but I was not able to find the same one.

我的问题是从向量x中找到m个元素的组合，但是m可能大于x.例如，从字母[1:2]中选择3个元素，希望它们可以返回:

My question is to find combinations of m number of elements from vector x, but m could be larger than x. For example, pick 3 elements from letters[1:2], which hopefully can return:

combn(letters[1:2],3)
       [,1]  [,2]  [,3]  [,4] 
[1,]   "a"   "a"   "a"    "b"
[2,]   "a"   "a"   "b"    "b"
[3,]   "a"   "b"   "b"    "b"

但是，组合函数n<中的错误；米有类似的功能，包括gtools:permutations，expand.grid.

But instead error in combn function n < m. There are similar functions including gtools:permutations, expand.grid.

如果有人之前曾问过同样的问题，请再次道歉，但我没有抓住.谢谢.

Apologize again if someone asked the same questions previously, but I did not catch it. Thanks.

推荐答案

为此专门构建了一些软件包.基本前提是我们需要重复长度为m的组合，其中m可能大于输入向量.我们从经典的gtools开始:

There are a few packages specifically built for this. The basic premise is that we need combinations with repetition of length m where m could be larger than the input vector. We start with the classic gtools:

library(gtools)
combinations(2, 3, letters[1:2], repeats.allowed = TRUE)
    [,1] [,2] [,3]
[1,] "a"  "a"  "a" 
[2,] "a"  "a"  "b" 
[3,] "a"  "b"  "b" 
[4,] "b"  "b"  "b"

然后是arrangements，它是iterpc(在上面的注释中由@Gregor链接的程序包)的替代物:

And then there is arrangements which is a replacement for iterpc (the package linked by @Gregor in the comments above):

library(arrangements)
arrangements::combinations(2, 3, letters[1:2], replace = TRUE)
     [,1] [,2] [,3]
[1,] "a"  "a"  "a" 
[2,] "a"  "a"  "b" 
[3,] "a"  "b"  "b" 
[4,] "b"  "b"  "b"

最后是我写的RcppAlgos:

library(RcppAlgos)
comboGeneral(letters[1:2], 3, TRUE)
     [,1] [,2] [,3]
[1,] "a"  "a"  "a" 
[2,] "a"  "a"  "b" 
[3,] "a"  "b"  "b" 
[4,] "b"  "b"  "b"

combn是一个很棒的功能，它作为R的基本软件包之一提供，但是其缺点之一是它不允许重复(这是此处所要求的).我写了一个非常全面的概述，概述了与此类似的问题，可以在这里找到:遍历R中的组合法学.

combn is an awesome function that ships as one of the base packages with R, however one of its shortcomings is that it doesn't allow repetition (which is what is required here). I wrote a pretty comprehensive overview for problems exactly like this one that can be found here: A Walk Through a Slice of Combinatorics in R.

这篇关于R找到所有可能的独特组合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！