函数combn()一次生成m个元素的所有组合.对于nCm small来说非常快速有效(其中n是x的元素数),但它很快就耗尽了内存.例如:
> combn(c(1:50), 12, simplify = TRUE)
Error in matrix(r, nrow = len.r, ncol = count) :
invalid 'ncol' value (too large or NA)
我想知道函数combn()是否可以修改,以便它只生成k个选择的组合.让我们将这个新函数调用为combn().然后我们会:
> combn(c("a", "b", "c", "d"), m=2)
[,1] [,2] [,3] [,4] [,5] [,6]
[1,] "a" "a" "a" "b" "b" "c"
[2,] "b" "c" "d" "c" "d" "d"
>chosencombn(c("a", "b", "c", "d"), m=2, i=c(1,4,6))
[,1] [,2] [,3]
[1,] "a" "b" "c"
[2,] "b" "c" "d"
>chosencombn(c("a", "b", "c", "d"), m=2, i=c(4,5))
[,1] [,2]
[1,] "b" "b" …