[Rcpp-devel] Datetime substraction bug ?

[Robin Girard]

I don't have any problem with Dirk's convention, and as Dirk said that should not create such a discussion (and it was not my intention to create one, just to point a problem I had if this can help others). 

However I think that your example is designed to miss my point. My point was that the syntax for the use of operator "-" is NOT "-(c(1,3))" but "1-3" which makes the logical assertion "(1-3)>0" true.  This is not what I would call a usual convention.

Nothing more to say. Still in deep addictive love with Rcpp...

R.


----- Mail original -----
De: "Patrick Burns" <patrick at burns-stat.com>
À: rcpp-devel at lists.r-forge.r-project.org
Envoyé: Mardi 2 Avril 2013 17:34:37
Objet: Re: [Rcpp-devel] Datetime substraction bug ?

In case Dirk is feeling lonely, I'll side with him.

I think the ultimate issue is abstraction versus
application.  In a purely abstract setting, then I
agree that `-`(1, 3) should be negative.  But we
don't have a purely abstract setting.  I agree with
Dirk's New Year's/Easter example -- if the dates are
in order, then the diff should be positive to my
mind.

Note also:

 > diff(c(1, 3))
[1] 2

Pat


On 02/04/2013 15:33, Romain Francois wrote:
> Le 30/03/13 00:44, Dirk Eddelbuettel a écrit :
>>
>> On 29 March 2013 at 23:37, Robin Girard wrote:
>> | Hi List
>> |
>> | why is it that we have in the Datetime definition
>> | (here
>> http://dirk.eddelbuettel.com/code/rcpp/html/Date_8cpp_source.html#l00271
>> )
>> |
>> | double operator-(const Datetime& d1, const Datetime& d2) { return
>> d2.m_dt - d1.m_dt; }
>> | bool operator<(const Datetime &d1, const Datetime& d2) { return
>> d1.m_dt < d2.m_dt; }
>> |
>> | I feel there is a contradiction
>> | substraction shoulb be d1.m_dt - d2.m_dt;  no ?
>>
>> It's been a while since I wrote that and I think I followed the
>> difftime()
>> convention in R. Or maybe not.  To me d1 comes before d2 in the way the
>> arguments are given, so d2 is larger and I want to subtract d1 from d2.
>
> Well. operator-(a, b) is supposed to implement a-b. See e.g. wikipedia
> http://en.wikipedia.org/wiki/Operators_in_C_and_C%2B%2B
>
> The current implementation does not make sense to me. So I second Robin
> here.
>
>> In any event, if it bugs you greatly you are always free to write your
>> own
>> function. ;-)
>>
>> Dirk
>
> wtf. This is the same as saying 3-1 = -2
>
> And if i follow your logic, why is the operator< implemented this way
> (correctly this time).
>
>> | Robin
>> |
>> | Dr. Girard Robin
>> | Chargé de Recherche
>> |
>> | MINES-ParisTech / Département Energétique et Procédés / PERSEE /
>> Groupe ERSEI
>> | Centre Procédés, Energies Renouvelables et Systèmes Energétiques
>> (PERSEE)
>> | Center for Processes, Renewables Energies and Energy Systems
>> | Renewable Energies & Smartgrids (ERSEI)
>> |
>> | 1 Rue Claude Daunesse - CS 10207 - F-06904 Sophia Antipolis Cedex
>> | Tel: +33.4.93.67.89.64 (~99), Fax: +33.4.93.95.75.35
>> | e-mail : robin.girard at mines-paristech.fr
>> |
>> | web page perso
>> http://www.mines-paristech.fr/Services/Annuaire/&?id=8828
>> | statoverflow : http://stats.stackexchange.com/users/223/robin-girard
>> | web page centre PERSEE : http://www.cep.mines-paristech.fr/
>> | linkedin : http://www.linkedin.com/profile/view?id=14907272&trk=tab_pro
>> |
>> | Le lien vaut mieux que le bien.
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-- 
Patrick Burns
patrick at burns-stat.com
http://www.burns-stat.com
http://www.portfolioprobe.com/blog
twitter: @burnsstat @portfolioprobe
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