Apologies if this belabors the point, but let's look at your second example to see why order and rank are different:
> x <- c(12,34,15,77,78,22) > names(x) <- 1:6 > x 1 2 3 4 5 6 12 34 15 77 78 22 I've added names to the values so we can watch how they change. If we sort the numbers we get them in increasing order with their original indices: > sort(x) 1 3 6 2 4 5 12 15 22 34 77 78 The values in are order and the names show where each value came from originally. That sequence of index values is exactly what order(x) gives you: > order(x) [1] 1 3 6 2 4 5 > x[order(x)] 1 3 6 2 4 5 12 15 22 34 77 78 The rank function gives you the relative size of the value, not its position in the original vector: > rank(x) 1 2 3 4 5 6 1 4 2 5 6 3 > x[rank(x)] 1 4 2 5 6 3 12 77 34 78 22 15 The second value has rank 4, but that is not its index which is 2. The value with index 4 is 77 so it shows up in the second position. ------------------------------------- David L Carlson Department of Anthropology Texas A&M University College Station, TX 77840-4352 -----Original Message----- From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of J Robertson-Burns Sent: Monday, April 27, 2015 2:34 PM To: Giorgio Garziano; r-help@r-project.org Subject: Re: [R] Question about base::rank results There is a blog post on this topic: http://www.portfolioprobe.com/2012/07/26/r-inferno-ism-order-is-not-rank/ Pat On 26/04/2015 09:17, Giorgio Garziano wrote: > Hi, > > I cannot understand why rank(x) behaves as outlined below. > Based on the results of first x vector values ranking, which is as expected > in my opinion, > I cannot explain the following results. > >> x <- c(12,34,15,77,78) >> x[rank(x)] > [1] 12 15 34 77 78 (OK) > >> x <- c(12,34,15,77,78,22) >> x[rank(x)] > [1] 12 77 34 78 22 15 (?) > >> x <- c(12,34,77,15,78) >> x[rank(x)] > [1] 12 77 15 34 78 (?) > > Please any feedback ? Thanks. > > BR, > > Giorgio Garziano > > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
