[R] order() function, decreasing=TRUE unexpected behaviour

[Hawthorne Beyer]

Thank you Jeff. You are correct. I am relieved it is my mistake. Apologies for bothering everyone. I will try harder next time!
Best wishes,
Hawthorne Beyer
University of Queensland


________________________________________
From: Jeff Newmiller [jdnewmil at dcn.davis.CA.us]
Sent: 17 November 2013 14:38
To: Hawthorne Beyer; r-help at r-project.org
Subject: Re: [R] order() function, decreasing=TRUE unexpected behaviour

I think you are confused, and there is no problem with the order function. Keep in mind that order returns the index values in a sequence such that when the result of the order function is used as indexes for the original sequence then the data will be sorted as desired. You may see the error of your ways more clearly if you use a vector of strings like c("b","a","c","d","e") instead of integer values.

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Hawthorne Beyer <h.beyer at uq.edu.au> wrote:
>There appears to be an issue with the decreasing=TRUE option on the
>order() function that indicates either a bug or perhaps a design flaw
>(potentially flawed because I would suggest the majority of users would
>expect different behaviour).
>
># demonstration of problem:
>x <- c(2,1,3,4,5)
>order(x)
>order(x, decreasing=TRUE)
>
>order(x) correctly reports the order as:
>2 1 3 4 5
>I expected the result for order(x, decreasing=TRUE) to be:
>4 5 3 2 1
>but the values actually reported are:
>5 4 3 1 2
>which is also the result of order(-x) (this may indicate a possible
>cause of this issue?).
>
>Thus, the decreasing=TRUE option in the order() function does not
>reverse the order of the values reported under the default of
>decreasing=FALSE in an example with no ties. If this behaviour is by
>design I am struggling to understand what purpose the decreasing=TRUE
>option serves and would like to suggest that this is not consistent
>with how many (most?) users would expect this option to work.
>
>Tested on R2.15.3 and 3.0.1 (both x86_64 linux-gnu) with identical
>results. I have also tried it on other series of numbers with the same
>result.
>
>Apologies if this has been discussed or reported elsewhere but I could
>not find any relevant posts. Perhaps I have failed to understand some
>fundamental issue? Sorry if this is me being dimwitted - it does seem
>hard to believe that there is a bug in a relatively straightforward
>r-base function. But I thought I would mention this as it could impact
>many people.
>
>Many thanks to all the R developers and R community for producing and
>supporting such an outstanding and invaluable product.
>Hawthorne Beyer
>University of Queensland
>
>
>       [[alternative HTML version deleted]]
>
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