如何从R中大小为N的数据帧中获取大小为n的所有可能的子样本？

Question

I have a dataframe with 20 classrooms [1 to 20] indexes and 20 different number of students in each class, how to obtain all sub-samples of size n = 8 and store them because i want to use them later for calculations. I used combn() but that takes only one vector, can i use it with a dataframe and how? (sorry but i'm new in R), dataframe below:

  classrooms students 1 1 29 2 2 30 3 3 35 4 4 28 5 5 32 6 6 20 7 7 25 8 8 22 9 9 32 10 10 26 11 11 27 12 12 34 13 13 27 14 14 28 15 15 33 16 16 21 17 17 36 18 18 24 19 19 19 20 20 32 

Answer 1

It is as simple as passing a function to combn . simplify = FALSE means that a list will be returned.

Assuming you want all possible combinations of 8 classrooms from the dataset classrooms

 combinations <- combn(nrow(classrooms), 8, function(x,data) data[x,], 
                  simplify = FALSE, data =classrooms )

 head(combinations, n = 2)

[[1]]
  classrooms students
1          1       29
2          2       30
3          3       35
4          4       28
5          5       32
6          6       20
7          7       25
8          8       22

[[2]]
  classrooms students
1          1       29
2          2       30
3          3       35
4          4       28
5          5       32
6          6       20
7          7       25
9          9       32