Time object problems - 1.8.2

[Greg Lorriman]

I am trying to efficiently get the date part of a Time object.

To remove the time part of the Time object I subtract the modulo of a
day-in-seconds. But if I do this I get a Time object of the date *plus
1 hour*!!! Perhaps I'm just tired, but I don;t understand why.

ie :

DAY_IN_SECS=60*60*24;
t=Time.parse("20-Oct-2005 04:04:00")
datePart=t-t.to_f.modulo(DAY_IN_SECS);

(and I might apply Time.at to get a Time object rather than a float.)

However, the result of the above is

20-Oct-2005 01:00:00

instead of

20-Oct-2005 00:00:00

Anyone got any ideas?

Greg

 

[Bernhard 'elven' Stoeckner]

Greg Lorriman scribbled on Wednesday 15 Mar 2006 12:55:

I am trying to efficiently get the date part of a Time object.

To remove the time part of the Time object I subtract the modulo of a
day-in-seconds. But if I do this I get a Time object of the date *plus
1 hour*!!! Perhaps I'm just tired, but I don;t understand why.

ie :

DAY_IN_SECS=60*60*24;
t=Time.parse("20-Oct-2005 04:04:00")
datePart=t-t.to_f.modulo(DAY_IN_SECS);

(and I might apply Time.at to get a Time object rather than a float.)

However, the result of the above is

20-Oct-2005 01:00:00

instead of

20-Oct-2005 00:00:00

Anyone got any ideas?

Greg

irb(main):001:0> t = Time.now; t - t.sec - 60 * t.min - 3600 * t.hour
=> Wed Mar 15 00:00:00 CET 2006

 

[Pit Capitain]

I am trying to efficiently get the date part of a Time object.

To remove the time part of the Time object I subtract the modulo of a
day-in-seconds. But if I do this I get a Time object of the date *plus
1 hour*!!! Perhaps I'm just tired, but I don;t understand why.

DAY_IN_SECS=60*60*24;
t=Time.parse("20-Oct-2005 04:04:00")
datePart=t-t.to_f.modulo(DAY_IN_SECS);

(and I might apply Time.at to get a Time object rather than a float.)

However, the result of the above is

20-Oct-2005 01:00:00

instead of

20-Oct-2005 00:00:00

Anyone got any ideas?

Greg, look at this:

p Time.at(0)

It starts at 1 o'clock.

Regards,
Pit

 

[Dimitri Aivaliotis]

Hi Greg,

I am trying to efficiently get the date part of a Time object.

I've just been playing around with Time and Date a bit. I have to ask: why=
?

You can get just the date part much more easily by using a Date object:

Date.parse("20-Oct-2005 04:04:00").to_s
=3D> "2005-10-20"

If you absolutely need a time object out of it, you can use 'facets':

require 'facet/date/to_time'
Date.parse("20-Oct-2005 04:04:00").to_time
=3D> Thu Oct 20 00:00:00 CEST 2005

HTH

- Dimitri

 

[Greg Lorriman]

I've just been playing around with Time and Date a bit. I have to ask: why?

You can get just the date part much more easily by using a Date object:

Unfortunately the Date class is horrifically slow. I'm already being
hammered by other slow aspects of ruby, which I can't avoid. So Time it
is!

 

[Dimitri Aivaliotis]

Unfortunately the Date class is horrifically slow. I'm already being
hammered by other slow aspects of ruby, which I can't avoid. So Time it
is!

Indeed. I just discovered
http://www.recentrambles.com/pragmatic/view/33 from another thread.=20
Interestingly enough, by replacing DateTime with Date in the example,
the benchmark comes out about 3 times faster. I guess having to work
with hours, minutes, and seconds is expensive.

- Dimitri

 

[Gordon Thiesfeld]

irb(main):001:0> t = Time.now; t - t.sec - 60 * t.min - 3600 * t.hour
=> Wed Mar 15 00:00:00 CET 2006

How about:

irb(main):001:0> t = Time.now; Time.local(t.year,t.month,t.day)
=> Wed Mar 15 00:00:00 Central Standard Time 2006

 

[Greg Lorriman]

It makes me think that an effort is needed to convert many of the
libraries that do basic heavy-lifting, like DateTime and CSV and
others, to C libraries.

I like the purity of the idea of a "pure Ruby" library, but I am
suffering the consequences and even considering jumping to Python; the
pain is getting to be too much.

 

[ara.t.howard]

It makes me think that an effort is needed to convert many of the
libraries that do basic heavy-lifting, like DateTime and CSV and
others, to C libraries.

I like the purity of the idea of a "pure Ruby" library, but I am
suffering the consequences and even considering jumping to Python; the
pain is getting to be too much.

check out the speed gains one can get with FasterCSV and reconsider - and it's
still pure ruby.

regards.

-a

 

[Greg Lorriman]

I like the purity of the idea of a "pure Ruby" library, but I am

check out the speed gains one can get with FasterCSV and reconsider - and it's
still pure ruby

Sounds promising. I particularly like the sound of "Faster", in
"FasterCSV".

thanks for that

Greg

 

[Greg Lorriman]

Anyone got any ideas?

Greg, look at this:

p Time.at(0)

It starts at 1 o'clock.

Unfathomable! What does it mean?!?! I am entirely perplexed by this
reality.

Greg

 

[Pit Capitain]

Unfathomable! What does it mean?!?! I am entirely perplexed by this
reality.

Greg, sorry for the noise. Time.at(0) is "epoch" (1970-01-01 00:00:00
GMT). My timezone is GMT + 1, so epoch happened to be at 1 o'clock. I
suppose that's the reason why your algorithm didn't work.

Regards,
Pit

 

[Greg Lorriman]

p Time.at(0)

Greg, sorry for the noise. Time.at(0) is "epoch" (1970-01-01 00:00:00
GMT). My timezone is GMT + 1, so epoch happened to be at 1 o'clock. I
suppose that's the reason why your algorithm didn't work.

Well that is the answer, then. Thankyou very much for that. Perhaps the
docs need expanding a little. I think even a computer scientist might
trip up on "epoch". I was thinking, in fact, that Time isn't a
practical Time/Date implementation and was possibly concieved in an
academic mind, which your observation would seem to confirm; I don't
think I've ever used such an awkward time/date implementation. However
I haven't used Date yet!!!

Greg