[Rcpp-devel] Datetime substraction bug ?

Robin Girard robin.girard at mines-paristech.fr
Sun Mar 31 11:52:05 CEST 2013

Actually that's not a big trick 
date.getFractionalTimestamp() returns date.m_dt which is a double. The substraction on double is the "usual one" and 
date_end.getFractionalTimestamp()-date_begin.getFractionalTimestamp() gives a positive number if and only if date_end>date_begin. 
My only regret is that it gives longer code line and less ease of reading. But I clearly understand that it's a matter of convention and if other have integrated this convention this cannot be changed now, otherwise it will become a bug for them...

at the end a "bug" is only a missinterpretation of something somewhere ? :) 

lots of .getFractionalTimestamp() everywhere for me ... 

----- Mail original -----
De: "stat quant" <statquant at outlook.com>
À: "Robin Girard" <robin.girard at mines-paristech.fr>
Cc: rcpp-devel at lists.r-forge.r-project.org
Envoyé: Dimanche 31 Mars 2013 11:32:08
Objet: Re: [Rcpp-devel] Datetime substraction bug ?

Thanks a lot for reporting this I would surely have been caught (may be I am I'll go through code I wrote using this) by this bug. 
Posting your workaround would not hurt I think... 

Thanks and cheers 

2013/3/30 Robin Girard < robin.girard at mines-paristech.fr > 

Thanks you're right I already wrote it myself with getFractional... 
and indeed that's not really what we should call a "bug" but it took me a while to understand that 

if date1-date2>0 then date1<date2 ;) 


----- Mail original ----- 
De: "Dirk Eddelbuettel" < edd at debian.org > 
À: "Robin Girard" < robin.girard at mines-paristech.fr > 
Cc: rcpp-devel at lists.r-forge.r-project.org 
Envoyé: Samedi 30 Mars 2013 00:44:08 
Objet: Re: [Rcpp-devel] Datetime substraction bug ? 

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. 

In any event, if it bugs you greatly you are always free to write your own 
function. ;-) 


| Robin 
| Dr. Girard Robin 
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