I want to find all the possible samples of two classes from the 5 different classes. I am trying this:
x <- c(A = 23, B = 21, C = 29, D = 17, E = 18)
mean (x)
sd (x)
sample(x)
sample(x, 2, replace = FALSE, prob = NULL)
sample(x, 5, replace = FALSE, prob = NULL)
but I think it is wrong it does not give me the number of all the possible samples
Try this
install.packages("gtools")
library(gtools)
permutations(length(x), 2, x)
# [,1] [,2]
# [1,] 17 18
# [2,] 17 21
# [3,] 17 23
# [4,] 17 29
# [5,] 18 17
# [6,] 18 21
# [7,] 18 23
# [8,] 18 29
# [9,] 21 17
# [10,] 21 18
# [11,] 21 23
# [12,] 21 29
# [13,] 23 17
# [14,] 23 18
# [15,] 23 21
# [16,] 23 29
# [17,] 29 17
# [18,] 29 18
# [19,] 29 21
# [20,] 29 23
If you just want to know the amount of possible permutations go with @Floo0s answer or do something like
nrow(permutations(length(x), 2, x))
# [1] 20
If you have 5 classes. There are 5 over 2 possibilities.
see http://en.wikipedia.org/wiki/Binomial_coefficient
In R this is what the function choose calculates.
So
choose(length(x),2)
Answer: 10 possible combinations (if the order does not matter, so (A,B) is equal to (B,A))
If the order matters it is
choose(length(x),2) * factorial(2)
Answer: 20
As Colonel Beauvel mentioned. To find all these combinations use combn
Maybe by using:
combn(x, 2)
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,] 23 23 23 23 21 21 21 29 29 17
[2,] 21 29 17 18 29 17 18 17 18 18
Columns of the matrix will give you all possible combinations ignoring order.
Or use package combinat.
