所有长度的无序组合 [英] Unordered combinations of all lengths

问题描述

我正在寻找一个函数，该函数可以将向量的所有无序组合返回给我.例如

I am looking a function that return me all the unordered combination of a vector. eg

x <- c('red','blue','black')
uncomb(x)
[1]'red'
[2]'blue'
[3]'black'
[4]'red','blue'
[5]'blue','black'
[6]'red','black'
[7]'red','blue','black'

我猜想某些库中有一个函数可以执行此操作，但是找不到.我正在尝试使用gtool的permutations，但这不是我想要的功能.

I guess that there is a function in some library that do this, but in can't find it. I am trying with permutations of gtool but it is not the function i am looking for.

推荐答案

您可以在combn()函数的m参数上应用长度为x的序列.

You could apply a sequence the length of x over the m argument of the combn() function.

x <- c("red", "blue", "black")
do.call(c, lapply(seq_along(x), combn, x = x, simplify = FALSE))
# [[1]]
# [1] "red"
# 
# [[2]]
# [1] "blue"
# 
# [[3]]
# [1] "black"
# 
# [[4]]
# [1] "red"  "blue"
# 
# [[5]]
# [1] "red"   "black"
# 
# [[6]]
# [1] "blue"  "black"
# 
# [[7]]
# [1] "red"   "blue"  "black"

如果您喜欢矩阵结果，则可以将stringi::stri_list2matrix()应用于上面的列表.

If you prefer a matrix result, then you can apply stringi::stri_list2matrix() to the list above.

stringi::stri_list2matrix(
    do.call(c, lapply(seq_along(x), combn, x = x, simplify = FALSE)),
    byrow = TRUE
)
#      [,1]    [,2]    [,3]   
# [1,] "red"   NA      NA     
# [2,] "blue"  NA      NA     
# [3,] "black" NA      NA     
# [4,] "red"   "blue"  NA     
# [5,] "red"   "black" NA     
# [6,] "blue"  "black" NA     
# [7,] "red"   "blue"  "black"

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