查找三个字符串的所有可能组合

Question

假设我有一些词根，前缀和后缀。

roots <- c("car insurance", "auto insurance")
prefix <- c("cheap", "budget")
suffix <- c("quote", "quotes")

R中是否有一个简单的函数或包可以构造 三个特征向量的所有可能组合。

所以我想要一个返回以下列表的列表，数据框或向量 每个字符串的所有可能组合。

cheap car insurance
budget car insurance
cheap car insurance quotes
cheap auto insurance quotes
auto insurance quote
auto insurance quotes
...

像“汽车保险报价”这样的东西，我只使用后缀而没有前缀，所以我需要得到这些结果的所有可能结果。

Answer 1

expand.grid是你的朋友：

expand.grid(prefix, roots, suffix)

    Var1           Var2   Var3
1  cheap  car insurance  quote
2 budget  car insurance  quote
3  cheap auto insurance  quote
4 budget auto insurance  quote
5  cheap  car insurance quotes
6 budget  car insurance quotes
7  cheap auto insurance quotes
8 budget auto insurance quotes

编辑包含Prasad的有用评论：

但是，您会注意到结果是因素而不是字符。要将这些因素转换为字符向量，您可以使用do.call和paste，如下所示：

do.call(paste, expand.grid(prefix, roots, suffix))

[1] "cheap car insurance quote"    "budget car insurance quote"  
[3] "cheap auto insurance quote"   "budget auto insurance quote" 
[5] "cheap car insurance quotes"   "budget car insurance quotes" 
[7] "cheap auto insurance quotes"  "budget auto insurance quotes"

Answer 2

您可以使用paste函数作为outer的参数：

outer(prefix,outer(roots,suffix,paste),paste)

输出：

, , 1

     [,1]                         [,2]                         
[1,] "cheap car insurance quote"  "cheap auto insurance quote" 
[2,] "budget car insurance quote" "budget auto insurance quote"

, , 2

     [,1]                          [,2]                          
[1,] "cheap car insurance quotes"  "cheap auto insurance quotes" 
[2,] "budget car insurance quotes" "budget auto insurance quotes"

可以使用as.vector将其缩小为单个矢量。