tips: r语言排列组合给定vector的特定元素

如果想要提取vector里面的3个元素的所有可能组合，怎么做？

1) r basic 

combn function - RDocumentation

2) combinations from gtools 

combinations function - RDocumentation

example:

example <- c("zhao","qian","sun", "li", "zhou", "wu")
 
combn(example, 2)
     [,1]   [,2]   [,3]   [,4]   [,5]   [,6]   [,7]   [,8]   [,9]   [,10]
[1,] "zhao" "zhao" "zhao" "zhao" "zhao" "qian" "qian" "qian" "qian" "sun"
[2,] "qian" "sun"  "li"   "zhou" "wu"   "sun"  "li"   "zhou" "wu"   "li" 
     [,11]  [,12] [,13]  [,14] [,15] 
[1,] "sun"  "sun" "li"   "li"  "zhou"
[2,] "zhou" "wu"  "zhou" "wu"  "wu"  
 
gtools::combinations(length(example), 2, example)
      [,1]   [,2]  
 [1,] "li"   "qian"
 [2,] "li"   "sun" 
 [3,] "li"   "wu"  
 [4,] "li"   "zhao"
 [5,] "li"   "zhou"
 [6,] "qian" "sun" 
 [7,] "qian" "wu"  
 [8,] "qian" "zhao"
 [9,] "qian" "zhou"
[10,] "sun"  "wu"  
[11,] "sun"  "zhao"
[12,] "sun"  "zhou"
[13,] "wu"   "zhao"
[14,] "wu"   "zhou"
[15,] "zhao" "zhou"