[datatable-help] Suggestion on ITime class implementing.

[Matthew Dowle]

Hi,

An alternative to POSIXct is integer time :

12:34:56.789  =>  123456789L

which I do quite a bit. And integer dates: 26 Mar 2013 => 20130326L.

You can get quite far with two integer columns: date and time. Quite 
often I don't use any DateTime class at all. Each column is 4 bytes and 
`roll=TRUE` then only rolls within the same day which is what I usually 
want.

But, yes ITime should be in milliseconds. I couldn't find this on the 
tracker so have now filed it here :
     
https://r-forge.r-project.org/tracker/index.php?func=detail&aid=2644&group_id=240&atid=978
If any links to posts or S.O. questions are not reachable from there, 
please add.

For micro (and nanosecond, why not) then perhaps we could use integer64 
to avoid any floating point issues.

24*60*60*1e9 * 365*100  ==  3.15e18

which fits in 2^63 (9.2e18), if I've got the arithmetic right.  The 
nano timestamp could be +/- 292 years of precise nanoseconds around the 
epoch.

And/or, for time only with no date, it could go to picoseconds :  
24*60*60*1e12 = 8.6e16 < 2^63

All that would be required is availability of integer64, which is 
pretty standard (even on 32bit machines).

Matthew


On 23.03.2013 07:06, gaizoule wrote:
> Hi, everyone,
> data.table is really a fantastic package,  I have become accustomed 
> to using
> it and saved a lot of time.
> In my daily work, I need to analysis lots of tick data,  the 
> IDateTime is
> very useful for me.  However, ITime class can not handle Millisecond. 
> I
> suggest using  the numbers of milliseconds to represents the introday 
> time,
> for example,  for time "11:00:00.000",  using  integer 11 * 60 * 60 * 
> 1000
> to represent it.  I have used kdb+/q ,  kdb+/q just do with time by 
> that
> way.
>
> best regards,
>
> gaizoule
>
>
>
>
> --
> View this message in context:
> 
> http://r.789695.n4.nabble.com/Suggestion-on-ITime-class-implementing-tp4662281.html
> Sent from the datatable-help mailing list archive at Nabble.com.
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