[R] I don't know the difference between rank and order

[(Ted Harding)]

On 21-Nov-2012 02:57:19 li1127217ye wrote:
> I don't know the difference between rank and order.For example:
>> x=c(10,30,30,20,10,20)
>> x[rank(x,ties.method="first")]
> [1] 10 10 20 30 30 20
>> x[order(x)]
> [1] 10 10 20 20 30 30
> 
> the result is quite different,
>  x[rank(x,ties.method="first")]
> [1] 10 10 20 30 30 20
> It is not sorted,why?

It is because rank() gives, for each element of x, the position
of that value within the sorted series of all the values in x.
This will not, in general, be the same as the index, within x,
of the value that should be in that position.

Example:

  x1=c(6,5,4,2,3,1)

  x1[rank(x1,ties.method="first")]
  # [1] 1 3 2 5 4 6

  rank(x1,ties.method="first")
  # [1] 6 5 4 2 3 1

So "2" indeed has rank 2, and "3" has rank 3; but what will be
returned by x1[rank(x)] will depend on what is in x[2] and x[3]
(in this case "5" and "4" respectively).

Ted.

-------------------------------------------------
E-Mail: (Ted Harding) <Ted.Harding at wlandres.net>
Date: 21-Nov-2012  Time: 08:13:23
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