Re: [udunits] Less pernickety version of ut_compare() ?

• To: Steve Emmerson <emmerson@xxxxxxxx>
• Subject: Re: [udunits] Less pernickety version of ut_compare() ?
• From: PIGUET Bruno <bruno.piguet@xxxxxxxx>
• Date: Tue, 11 Aug 2015 18:14:37 +0200 (CEST)

Steve, 

Just did what you suggested. 

The code I attached to my mail is now on 
https://gist.github.com/piguet-b/271f856cdd8d45bd6105 

Quite far from being of sufficient quality to be included in the library, but I 
hope it helps see the point I suggest. 

Bruno. 
-- 
Bruno Piguet 
Météo-France 
Équipe GMEI/TRAMM 
CNRM/GAME, UMR3589 CNRS/Météo-France 
Fixe : +33 561079659 
Postal : 42 Av. G. Coriolis 
31057 Toulouse CEDEX 1 


----- Mail original -----

De: "Steve Emmerson" <emmerson@xxxxxxxx> 
À: "PIGUET Bruno" <bruno.piguet@xxxxxxxx> 
Cc: udunits@xxxxxxxxxxxxxxxx 
Envoyé: Mardi 11 Août 2015 17:04:42 
Objet: Re: [udunits] Less pernickety version of ut_compare() ? 

Bruno, 

Interesting idea. I've added it to the list of issues at the UDUNITS GitHub 
site . You should go there and subscribe to the issue. 

I suppose a ut_tolerant_compare() function could first test to see if the units 
are compatible and, if they are, convert values in one unit to the other to 
determine if they are close to one another. 

Why don't you post your ut_tolerant_compare() function to the GitHub site. 

Regards, 
Steve Emmerson 

On Tue, Aug 11, 2015 at 6:34 AM, PIGUET Bruno < bruno.piguet@xxxxxxxx > wrote: 


Hi, 

I found the ut_compare() function, as currently existing the the udunits2 
library, to be too strict for my needs. 

In particular, for some units, the comparison between the original unit and a 
back-and-forth transformation to text expression fails. 
In other words : for some values of unit, ut_compare(unit, 
(ut_parse(ut_format(unit))) != 0. 

I know that a decimal textual representation of a real number cannot be exact, 
but I believe that we can safely assume that two units whose relative 
difference is less than 10^-8 or 10^-10 are identical. 
So, I wrote my own, more tolerant, ut_compare function (see attached source 
code). 

My questions are : 
- is this pernickety behaviour intended, or did someone just wrote the test 
"a==b" for floating-point values instead of the usual approximate test ? 
- Am I the only one interested in a more lenient version of ut_compare() ? 
Would it be a good idea to add a ut_tolerant_compare() function to the udunits2 
library ? 

Regards, 

Bruno. 

-- 
Bruno Piguet 
Météo-France 
Équipe GMEI/TRAMM 
CNRM/GAME, UMR3589 CNRS/Météo-France 
Fixe : +33 561079659 
Fax : +33 561079627 
Postal : 42 Av. G. Coriolis 
31057 Toulouse CEDEX 1 



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• References:
  • [udunits] Less pernickety version of ut_compare() ?
    • From: PIGUET Bruno
  • Re: [udunits] Less pernickety version of ut_compare() ?
    • From: Steve Emmerson