Finding all possible combinations of a three strings

Let's say I have a couple roots, prefixes, and suffixes.

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

Is there a simple function or package in R which will allow me to construct all possible combinations of the three character vectors.

So I want a list, data frame, or vector which returns the following list of all possible combinations of each string.

cheap car insurance
budget car insurance
cheap car insurance quotes
cheap auto insurance开发者_开发百科 quotes
auto insurance quote
auto insurance quotes
...

With something like 'auto insurance quotes', I'm using just the suffix and no prefix, so I need to get all possible results of those outcomes also.

expand.grid is your friend:

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

Edited to include helpful comments by Prasad:

However, you will notice that your results are factors and not characters. To convert these factors into character vectors, you can use do.call and paste as follows:

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"

You can use a paste function as an argument to outer:

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

Output:

, , 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"

This can be reduced to a single vector using as.vector.