[R] [External] Weird behaviour of order() when having multiple ties

Avi Gross @v|gro@@ @end|ng |rom ver|zon@net
Mon Jan 31 18:32:47 CET 2022


Tim,
I thought I saw someone tell you that the order in which EQUAL items are presented is not deterministic in that any order, whether given by order() or sort() or anything else, is VALID.
Unless you supply additional constraints such as a second key to sort by, then the order becomes deterministic up to the point where both the keys are the same.
Here is a dumb suggestion. Place your Dat1 vector in a data.frame alongside another vector of 1:length(Dat1) and use some method that orders by Dat1 and then by the second vector, ascending. You have now forced it to take the first of a matching set before any others. 
Let me try another. Say I give you a problem that might have multiple answer such as a quadratic equation with solutions of 2 and 10. You ask me for AN answer and I say 10. Am I wrong? You ask me for all answers and I say [10,2] and someone else says [2,10] and you wonder which of us is right. Well we are both right. The proper way to test is not to ask if the lists or tuples or anything ordered is equivalent but to use something like a set and show that they are equivalent or something like one is a subset of the other both ways. 
Back to your topic, you are suggesting two independent developers should come up with algorithms to solve similar but different tasks the same way. Do you have any idea how many methods there are for sorting things? This site lists eleven and I am sure there are many more.
https://www.javatpoint.com/sorting-algorithms
What is considered more important is choosing an algorithm that works well on the kinds of data and some of those methods do not keep the data in the same order and produce results in the same order.
What you are pointing out is not an error but an inconsistency. The message to you is to not depend on a UNIQUE solution.


-----Original Message-----
From: Ebert,Timothy Aaron <tebert using ufl.edu>
To: Martin Maechler <maechler using stat.math.ethz.ch>; Stefan Fleck <stefan.b.fleck using gmail.com>
Cc: r-help using r-project.org <r-help using r-project.org>
Sent: Mon, Jan 31, 2022 10:07 am
Subject: Re: [R] [External] Weird behaviour of order() when having multiple ties

Dat1 <- c(0.6, 0.5, 0.3, 0.2, 0.1, 0.1, 0.2)
print(order(Dat1))
print(sort(Dat1))

Compare output



-----Original Message-----
From: R-help <r-help-bounces using r-project.org> On Behalf Of Martin Maechler
Sent: Monday, January 31, 2022 9:04 AM
To: Stefan Fleck <stefan.b.fleck using gmail.com>
Cc: r-help using r-project.org
Subject: Re: [R] [External] Weird behaviour of order() when having multiple ties

[External Email]

>>>>> Stefan Fleck
>>>>>    on Sun, 30 Jan 2022 21:07:19 +0100 writes:

    > it's not about the sort order of the ties, shouldn't all the 1s in
    > order(c(2,3,4,1,1,1,1,1)) come before 2,3,4? because that's not what
    > happening

aaah.. now we are getting somewhere:
It looks you have always confused order() with sort() ...
have you ?


    > On Sun, Jan 30, 2022 at 9:00 PM Richard M. Heiberger <rmh using temple.edu> wrote:

    >> when there are ties it doesn't matter which is first.
    >> in a situation where it does matter, you will need a tiebreaker column.
    >> ------------------------------
    >> *From:* R-help <r-help-bounces using r-project.org> on behalf of Stefan Fleck <
    >> stefan.b.fleck using gmail.com>
    >> *Sent:* Sunday, January 30, 2022 4:16:44 AM
    >> *To:* r-help using r-project.org <r-help using r-project.org>
    >> *Subject:* [External] [R] Weird behaviour of order() when having multiple
    >> ties
    >>
    >> I am experiencing a weird behavior of `order()` for numeric vectors. I
    >> tested on 3.6.2 and 4.1.2 for windows and R 4.0.2 on ubuntu. Can anyone
    >> confirm?
    >>
    >> order(
    >> c(
    >> 0.6,
    >> 0.5,
    >> 0.3,
    >> 0.2,
    >> 0.1,
    >> 0.1
    >> )
    >> )
    >> ## Result [should be in order]
    >> [1] 5 6 4 3 2 1
    >>
    >> The sort order is obviously wrong. This only occurs if i have multiple
    >> ties. The problem does _not_ occur for decreasing = TRUE.
    >>
    >> [[alternative HTML version deleted]]
    >>
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PLEASE do read the posting guide https://urldefense.proofpoint.com/v2/url?u=http-3A__www.R-2Dproject.org_posting-2Dguide.html&d=DwICAg&c=sJ6xIWYx-zLMB3EPkvcnVg&r=9PEhQh2kVeAsRzsn7AkP-g&m=LETnyM_0QTFNEMNectANV0IJZgIOyofIv54iJDPBZF-atb3Xe9lGTZ7tN68hw3Te&s=6QEl5w7lJHJJELW6QwypJN8KK64mDcTZXg5yoLs9Wu4&e=
and provide commented, minimal, self-contained, reproducible code.

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and provide commented, minimal, self-contained, reproducible code.

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