R rookies often confuse rank with order. It’s OK because they are truly confusing, and both of them give users “ranking” information. The following article elaborates how they are different.

Let’s take an easy example to show the mechanisms. Consider the situation that only one vector is given.

set.seed(1)
rate <- sample(10, 5)
rate
# 3 4 5 7 2
order(rate)
# 5 1 2 3 4
rank(rate)
# 2 3 4 5 1

Now, what order gives you is, in this example, that “the 5th element of rate is the smallest one”, so you have 5 coming in the first. order accepts multiple vectors as input arguments to break ties. Thus, for order function, you can do something like this:

rate[order(rate)]
# 2 3 4 5 7
# Permute "rate" in ascending order

On the other hand, rank gives you that “the rank of the last element among rate elements is the 1st”, so the 5th returned value is 1.

Besides order and rank, we have sort in R to sort a vector into orders. In this example, sort(rate) is equivalent to rate[order(rate)].

By default, all these three functions return an ascending order.

I know it takes some time to digest. Take it easy and feel free to ask further questions. :)