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