Re: DT::Duration overloads
Dave Rolsky wrote: Also, I'd like to point out that this really doesn't have as much to do with the internals as it does with the nature of date & time math. You cannot expect to understand date math without understanding that it's not possible to convert between various units of date/time, in particular from months to days or vice versa. This would be a problem regardless of the internals, right? I do understand the ambiguities when you are dealing with various forms of durations that are not anchored to an actual point in time. As I said in my last message, however, we're talking about two absolute points in time -- no ambiguity. Rephrased, the question is again: what is the midpoint of a span? (and if we come up with a good approach to this problem, it should solve the general class of problems having to do with portioning out spans). It's not immediately apparent to me what the solution is -- I know what I want to do, and would prefer it to be fairly easy and straightforward. This seems to be an area of the interface that could use some brushing up rather than some intrinsic ambiguity of date math. (I'm willing to meditate on possible solutions myself -- I'm not merely asking you to solve it for me. However, I just thought I might be missing something obvious) Thanks again, Matt
Re: DT::Duration overloads
Dave Rolsky wrote: Well, if you just want the _date_, it's pretty easy. my $dur = $dt1->delta_days($dt2); # or use Math::Round if you want my $mid = $dt1->add( days => int( $dur->delta_days / 2 ) ); If you want to account for the time then it gets funkier. Hmm, indeed. I need to approximate solar noon by deriving the midpoint between sunrise and sunset. I also need to approximate solar midnight by looking at the sunset from the prior day. As a general problem, finding a fractional time between two points in time is not that unusual. I *suppose* I could convert to epoch, take the diff, and use that to create a new duration. But it seems unfortunate that I'd have to step out of the datetime API like that. The two endpoints are known quantities -- there is no abiguity in selecting a midpoint. Is this sort of thing something that should exist in spans rather than expecting regular date math to handle? Matt
Re: DT::Duration overloads
On Thu, 10 Jun 2004, Matt Sisk wrote: > What I'd like to do is simply find the midpoint, more or less, between > two arbitrary datetimes. Off the cuff, knowing nothing about the > internals (which I do, but I'm pretending not to) I'd think this: Also, I'd like to point out that this really doesn't have as much to do with the internals as it does with the nature of date & time math. You cannot expect to understand date math without understanding that it's not possible to convert between various units of date/time, in particular from months to days or vice versa. This would be a problem regardless of the internals, right? -dave /*=== House Absolute Consulting www.houseabsolute.com ===*/
Re: DT::Duration overloads
On Thu, 10 Jun 2004, Matt Sisk wrote: > What I'd like to do is simply find the midpoint, more or less, between > two arbitrary datetimes. Off the cuff, knowing nothing about the > internals (which I do, but I'm pretending not to) I'd think this: > > $mid = $dt1 + ($dt2 - $dt1)/2 > > to dwim. > > However, as you say, things aren't really well defined the way durations > are defined internally at the moment. > > So the question becomes -- if the above is not the datetime idiom for > finding a midpoint between two datetimes, then what is? Well, if you just want the _date_, it's pretty easy. my $dur = $dt1->delta_days($dt2); # or use Math::Round if you want my $mid = $dt1->add( days => int( $dur->delta_days / 2 ) ); If you want to account for the time then it gets funkier. -dave /*=== House Absolute Consulting www.houseabsolute.com ===*/
Re: DT::Duration overloads
Dave Rolsky wrote: Thinking about this more, I'm considering maybe just requiring that multiplication be passed an integer, because if you do this: What I'd like to do is simply find the midpoint, more or less, between two arbitrary datetimes. Off the cuff, knowing nothing about the internals (which I do, but I'm pretending not to) I'd think this: $mid = $dt1 + ($dt2 - $dt1)/2 to dwim. However, as you say, things aren't really well defined the way durations are defined internally at the moment. So the question becomes -- if the above is not the datetime idiom for finding a midpoint between two datetimes, then what is? Thanks, Matt
Re: DT::Duration overloads
On Wed, 9 Jun 2004, Matt Sisk wrote: > I understand that division can be expressed as multiplication, but is > there any particular reason why division (/) is not overloaded but > multiplication is for durations? Then you could say: > > $midpoint = ($dt2 - $dt1)/2; > > rather than > > $midpoint = ($dt2 - $dt1) * 0.5; > > Small thing. Just curious. Thinking about this more, I'm considering maybe just requiring that multiplication be passed an integer, because if you do this: my $dur = DateTime::Duration->new( months => 1, days => 1, minutes => 1 ); $dur->multiple(.5); print DateTime->now->add_duration($dur)->datetime; The results are kind of weird, and certainly not what anyone would expect. -dave /*=== House Absolute Consulting www.houseabsolute.com ===*/
Re: DT::Duration overloads
On Thu, 10 Jun 2004, Rick Measham wrote: > On 10 Jun 2004, at 9:25 AM, Dave Rolsky wrote: > > What is half a minute? How long is half a month? > > $dtd = DateTime::Duration->new( > months => 1, > minutes => 1, > ); > > $half_dtd = $dtd / 2; > > print $half_dtd->months . "\n"; > # 0.5 > > print $half_dtd->seconds . "\n"; > # 0.5 > > print strfduration( > normalise => 'ISO', > pattern => '%Y years, %m months, %e days, %H hours, %M minutes, %S > seconds', > duration => $half_dtd > ); > # 0 years, 0 months, 15 days, 0 hours, 0 minutes, 30 seconds Great, now what should DateTime.pm do in the add_duration method? -dave /*=== House Absolute Consulting www.houseabsolute.com ===*/
Re: DT::Duration overloads
On 10 Jun 2004, at 9:25 AM, Dave Rolsky wrote: What is half a minute? How long is half a month? $dtd = DateTime::Duration->new( months => 1, minutes => 1, ); $half_dtd = $dtd / 2; print $half_dtd->months . "\n"; # 0.5 print $half_dtd->seconds . "\n"; # 0.5 print strfduration( normalise => 'ISO', pattern => '%Y years, %m months, %e days, %H hours, %M minutes, %S seconds', duration => $half_dtd ); # 0 years, 0 months, 15 days, 0 hours, 0 minutes, 30 seconds Senior Developer PrintSupply - Print Procurement & Supply Management 18 Greenaway Street VIC 3105 Tel: (03) 9850 3255 Fx: (03) 9850 3277 http://www.printsupply.com.au/
Re: DT::Duration overloads
On Wed, 9 Jun 2004, Matt Sisk wrote: > I understand that division can be expressed as multiplication, but is > there any particular reason why division (/) is not overloaded but > multiplication is for durations? Then you could say: > > $midpoint = ($dt2 - $dt1)/2; > > rather than > > $midpoint = ($dt2 - $dt1) * 0.5; > > Small thing. Just curious. Well, division doesn't really work, whether you do it as multiplication or not ;) What is half a minute? How long is half a month? -dave /*=== House Absolute Consulting www.houseabsolute.com ===*/
DT::Duration overloads
I understand that division can be expressed as multiplication, but is there any particular reason why division (/) is not overloaded but multiplication is for durations? Then you could say: $midpoint = ($dt2 - $dt1)/2; rather than $midpoint = ($dt2 - $dt1) * 0.5; Small thing. Just curious. Thanks, Matt
