expand.grid的非冗余版本 [英] Non-redundant version of expand.grid

问题描述

R 函数 expand.grid 返回提供的参数元素之间的所有可能组合。例如，

The R function expand.grid returns all possible combination between the elements of supplied parameters. e.g.

> expand.grid(c("aa", "ab", "cc"), c("aa", "ab", "cc"))
  Var1 Var2
1   aa   aa
2   ab   aa
3   cc   aa
4   aa   ab
5   ab   ab
6   cc   ab
7   aa   cc
8   ab   cc
9   cc   cc

您知道一种直接获取有效的方法的方法（因此在<$之后无需进行任何行比较c $ c> expand.grid ）仅提供的向量之间的唯一组合？输出将为

Do you know an efficient way to get directly (so without any row comparison after expand.grid) only the 'unique' combinations between the supplied vectors? The output will be

  Var1 Var2
1   aa   aa
2   ab   aa
3   cc   aa
5   ab   ab
6   cc   ab
9   cc   cc

编辑最终可以从答案中删除每个元素与其自身的组合。即使（数学上） aa aa 在 Var1 <的一个元素之间是（常规）唯一组合，我实际上也不在程序中使用它/ code>和另一个 var2 。

EDIT the combination of each element with itself could be eventually discarded from the answer. I don't actually need it in my program even though (mathematically) aa aa would be one (regular) unique combination between one element of Var1 and another of var2.

该解决方案需要从两个向量中生成元素对（即每个输入向量中的一个-以便可以将其应用于2个以上输入）

The solution needs to produce pairs of elements from both vectors (i.e. one from each of the input vectors - so that it could be applied to more than 2 inputs)

推荐答案

如何使用外部？但是这个特殊的函数将它们连接成一个字符串。

How about using outer? But this particular function concatenates them into one character string.

outer( c("aa", "ab", "cc"), c("aa", "ab", "cc") , "paste" )
#     [,1]    [,2]    [,3]   
#[1,] "aa aa" "aa ab" "aa cc"
#[2,] "ab aa" "ab ab" "ab cc"
#[3,] "cc aa" "cc ab" "cc cc"

您也可以在 combn 上使用如果不想重复元素，则是两个向量的唯一元素（例如 aa aa ）

You can also use combn on the unique elements of the two vectors if you don't want the repeating elements (e.g. aa aa)

vals <- c( c("aa", "ab", "cc"), c("aa", "ab", "cc") )
vals <- unique( vals )
combn( vals , 2 )
#     [,1] [,2] [,3]
#[1,] "aa" "aa" "ab"
#[2,] "ab" "cc" "cc"

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