[R] I don't understand the 'order' function

[Sarah Goslee]

Hi Julio,

On Tue, Apr 16, 2013 at 1:51 PM, Julio Sergio <juliosergio at gmail.com> wrote:
> I thought I've understood the 'order' function, using simple examples like:
>
>    order(c(5,4,-2))
>    [1] 3 2 1
>
> However, I arrived to the following example:
>
>    order(c(2465, 2255, 2085, 1545, 1335, 1210, 920, 210, 210, 505, 1045))
>    [1]  8  9 10  7 11  6  5  4  3  2  1
>
> and I was completely perplexed!
> Shouldn't the output vector be  11 10 9 8 7 6 4 1 2 3 5 ?
> Do I have a damaged version of R?

Your version of R is fine; your understanding is damaged. :)

order() returns the element indices for each position. So in your
example, the sorted version of the vector would have element 8 in the
first place, element 9 in the second place, and element 1 in the last
place. order() is not the same as rank().

See:
x <- c(2465, 2255, 2085, 1545, 1335, 1210, 920, 210, 210, 505, 1045)
order(x)
x[order(x)]
rank(x) # what you seem to expect

Sarah

-- 
Sarah Goslee
http://www.functionaldiversity.org