i am having trouble understanding the difference between the R function rank and the R function order. they seem to produce the same output:
> rank(c(10,30,20,50,40))
[1] 1 3 2 5 4
> order(c(10,30,20,50,40))
[1] 1 3 2 5 4
Could somebody shed some light on this for me? Thanks
Answer
> set.seed(1)
> x <- sample(1:50, 30)
> x
[1] 14 19 28 43 10 41 42 29 27 3 9 7 44 15 48 18 25 33 13 34 47 39 49 4 30 46 1 40 20 8
> rank(x)
[1] 9 12 16 25 7 23 24 17 15 2 6 4 26 10 29 11 14 19 8 20 28 21 30 3 18 27 1 22 13 5
> order(x)
[1] 27 10 24 12 30 11 5 19 1 14 16 2 29 17 9 3 8 25 18 20 22 28 6 7 4 13 26 21 15 23
rank returns a vector with the "rank" of each value. the number in the first position is the 9th lowest. order returns the indices that would put the initial vector x in order.
The 27th value of x is the lowest, so 27 is the first element of order(x) - and if you look at rank(x), the 27th element is 1.
> x[order(x)]
[1] 1 3 4 7 8 9 10 13 14 15 18 19 20 25 27 28 29 30 33 34 39 40 41 42 43 44 46 47 48 49