Re: [R] Class for time of day?
On Thu, May 21, 2009 at 8:28 PM, Gabor Grothendieck ggrothendi...@gmail.com wrote: It uses hours/minutes/seconds for values 1 day and uses days and fractions of a day otherwise. Yes, my examples were documenting this idiosyncracy. For values and operations that it has not considered it falls back to the internal representation. Yes, my examples were documenting this bad behavior. Most of your examples start to make sense once you realize this. Of course I realize this. That was the point of my examples. I understand perfectly well what is *causing* the bad behavior. That doesn't make it less bad. What is the point of a class system if functions ignore the class and perform meaningless calculations on the internal representation? -s [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Class for time of day?
You could create a subclass of times with its own print and format methods that printed and formatted hours/minutes/seconds even if greater than one day if that is the main item you need. Regarding division you could contribute that to the chron package. I've contributed a few missing items and they were incorporated. Giving an error when it does not understand something would be dangerous as it could break much existing code so that would probably not be possible at this stage. The idea of defaulting to internal representations is based on the idea that you get many features for free since the way the internal representations work gives the right answer in many cases. Its best to stick with the implicit philosophy that underlies a package. If you want a different philosophy then its really tantamount to creating a new package. I don't think that one is right and the other wrong but simply represent different viewpoints. On Fri, May 22, 2009 at 9:33 AM, Stavros Macrakis macra...@alum.mit.edu wrote: On Thu, May 21, 2009 at 8:28 PM, Gabor Grothendieck ggrothendi...@gmail.com wrote: It uses hours/minutes/seconds for values 1 day and uses days and fractions of a day otherwise. Yes, my examples were documenting this idiosyncracy. For values and operations that it has not considered it falls back to the internal representation. Yes, my examples were documenting this bad behavior. Most of your examples start to make sense once you realize this. Of course I realize this. That was the point of my examples. I understand perfectly well what is *causing* the bad behavior. That doesn't make it less bad. What is the point of a class system if functions ignore the class and perform meaningless calculations on the internal representation? -s __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Class for time of day?
On Fri, May 22, 2009 at 10:03 AM, Gabor Grothendieck ggrothendi...@gmail.com wrote: Regarding division you could contribute that to the chron package. I've contributed a few missing items and they were incorporated. Good to know. Maybe I'll do that Giving an error when it does not understand something would be dangerous as it could break much existing code so that would probably not be possible at this stage. But would it break any existing *correct* code? I find it hard to imagine any cases where adding 1 hour of difftime to times(12:00:00) should return 1.5 days rather than 13:00:00. The idea of defaulting to internal representations is based on the idea that you get many features for free since the way the internal representations work gives the right answer in many cases. I must admit I am rather shocked by this approach. Getting something for free is a bad bargain if what you get is nonsense. Its best to stick with the implicit philosophy that underlies a package. If you want a different philosophy then its really tantamount to creating a new package. I don't think that one is right and the other wrong but simply represent different viewpoints. So you would defend the viewpoint that 1 hour is the same thing as 1 day? -s [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Class for time of day?
On Fri, May 22, 2009 at 11:01 AM, Stavros Macrakis macra...@alum.mit.edu wrote: On Fri, May 22, 2009 at 10:03 AM, Gabor Grothendieck ggrothendi...@gmail.com wrote: Regarding division you could contribute that to the chron package. I've contributed a few missing items and they were incorporated. Good to know. Maybe I'll do that Giving an error when it does not understand something would be dangerous as it could break much existing code so that would probably not be possible at this stage. But would it break any existing *correct* code? I find it hard to imagine any cases where adding 1 hour of difftime to times(12:00:00) should return 1.5 days rather than 13:00:00. The idea of defaulting to internal representations is based on the idea that you get many features for free since the way the internal representations work gives the right answer in many cases. I must admit I am rather shocked by this approach. Getting something for free is a bad bargain if what you get is nonsense. Its best to stick with the implicit philosophy that underlies a package. If you want a different philosophy then its really tantamount to creating a new package. I don't think that one is right and the other wrong but simply represent different viewpoints. So you would defend the viewpoint that 1 hour is the same thing as 1 day? The way this might appear in code is if someone wanted to calculate the number of one hour intervals in 18 hours. One could write: t18 - times(18:00:00) t1 - times(1:00:00) as.numeric(t18) / as.numeric(t1) but since we all know that it uses internal representations unless it indicates otherwise a typical code snippet might shorten it to: as.numeric(t18 / t1) and all such code would break if one were to cause that to generate an error. (I think it would be ok if it generated a numeric automatically and that was the enhancement I had suggested to you.) You can try to argue that the user should not code that way but a huge amount of chron code exists by now (note that chron may pre-date R). If it were a new package one could consider raising new errors but at this point in time it would be unwise. __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Class for time of day?
On Fri, May 22, 2009 at 12:28 PM, Gabor Grothendieck ggrothendi...@gmail.com wrote: ...The way this might appear in code is if someone wanted to calculate the number of one hour intervals in 18 hours. One could write: t18 - times(18:00:00) t1 - times(1:00:00) as.numeric(t18) / as.numeric(t1) but since we all know that it uses internal representations unless it indicates otherwise Um, yes, I suppose that was the attitude in the 60's and 70's, but I think we have moved on from there. cf. http://en.wikipedia.org/wiki/Data_abstraction a typical code snippet might shorten it to: as.numeric(t18 / t1) and all such code would break if one were to cause that to generate an error. (18/24 day)/(1/24 day) is the perfectly meaningful dimensionless number 18, so this code should not break with a correct implementation of '/'. (cf. http://en.wikipedia.org/wiki/Dimensional_analysis). Alas, chron gives the nonsense result of 18 days. -s [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Class for time of day?
On Fri, May 22, 2009 at 1:55 PM, Stavros Macrakis macra...@alum.mit.edu wrote: On Fri, May 22, 2009 at 12:28 PM, Gabor Grothendieck ggrothendi...@gmail.com wrote: ...The way this might appear in code is if someone wanted to calculate the number of one hour intervals in 18 hours. One could write: t18 - times(18:00:00) t1 - times(1:00:00) as.numeric(t18) / as.numeric(t1) but since we all know that it uses internal representations unless it indicates otherwise Um, yes, I suppose that was the attitude in the 60's and 70's, but I think we have moved on from there. cf. http://en.wikipedia.org/wiki/Data_abstraction a typical code snippet might shorten it to: as.numeric(t18 / t1) and all such code would break if one were to cause that to generate an error. (18/24 day)/(1/24 day) is the perfectly meaningful dimensionless number 18, so this code should not break with a correct implementation of '/'. (cf. http://en.wikipedia.org/wiki/Dimensional_analysis). Alas, chron gives the nonsense result of 18 days. Your point was that otherwise undefined operations should produce an error and I was illustrating why that could not be introduced at this stage. I had already suggested that you implement division if you found it important and that was not the source of any disagreement. __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Class for time of day?
On Wed, May 20, 2009 at 12:28 PM, Gabor Grothendieck
ggrothendi...@gmail.com wrote:
There is a times class in the chron package.
Perfect! Just what I was looking for.
On Wed, May 20, 2009 at 12:19 PM, jim holtman jholt...@gmail.com wrote:
If you want the hours from a POSIXct, here is one way of doing it...
y - difftime(x, trunc(x, units='days'), units='hours')
Ah, trunc.POSIXt -- I missed that one, thanks.
It depends on what type of computations you want to do with it. You can
leave it as POSIXct and carry out a lot of them. Can you specify what you
want?
I am comparing irregular time series from different days, looking at the
differences in intraday patterns. So I want to put them on a common 0-24h
scale and then do various kinds of plots and analyses, keeping the
conventional display form (10:30 etc.) when specific times display or
print. It looks as though chron:::times combined with trunc.POSIXt pretty
much solves my problem, except that `times` ignores the time units:
as.POSIXct('2009-3-23 12:23')-trunc(as.POSIXct('2009-3-23 12:23'),day)
Time difference of 12.38333 hours
times(as.POSIXct('2009-3-23 12:23')-trunc(as.POSIXct('2009-3-23
12:23'),day))
Time in days: seems to treat difftimes as raw numbers!!
[1] 12.38333
Obviously I can work around this, but shouldn't `times` give an error when
it encounters an object of unknown class rather than unsafely using its
internal representation? Of course, better still if `times` converted
correctly
In general, `times` has other inconsistent and peculiar behavior:
times(2) = Time in days: 2Allows specifying multi-day periods, OK
times(1.5) = Time in days: 1.5 Allows specifying fractional multi-day
periods, OK
times(0.5) = 12:00:00 Inconsistent format compared to times(1.5)
times(18:00:00) + times(18:00:00) = Time in days: 1.5, OK
times(36:00:00) = error Why does it allow times(1.5) and
times(18:00:00) + times(18:00:00) to specify 1.5 days, but not 36 hours?
times(-0.5) = -0.5 Why doesn't it print Time in days: -0.5?
times(18:00:00)/times(1:00:00) = Time in days: 18Incorrect
dimensions; meaningless result -- should be dimensionless
times(18:00:00) * times(10:00:00) = 07:30:00 Incorrect dimensions;
meaningless result.
sin(times(18:00:00)) = 16:21:34 Meaningless result -- should be error
It's nice that R has a class system, but if code ignores the class
There is an article on dates and times in R News 4/1.
Thanks for the pointer.
-s
[[alternative HTML version deleted]]
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Re: [R] Class for time of day?
On Thu, May 21, 2009 at 5:04 PM, Stavros Macrakis macra...@alum.mit.edu wrote:
On Wed, May 20, 2009 at 12:28 PM, Gabor Grothendieck
ggrothendi...@gmail.com wrote:
There is a times class in the chron package.
Perfect! Just what I was looking for.
On Wed, May 20, 2009 at 12:19 PM, jim holtman jholt...@gmail.com wrote:
If you want the hours from a POSIXct, here is one way of doing it...
y - difftime(x, trunc(x, units='days'), units='hours')
Ah, trunc.POSIXt -- I missed that one, thanks.
It depends on what type of computations you want to do with it. You can
leave it as POSIXct and carry out a lot of them. Can you specify what you
want?
I am comparing irregular time series from different days, looking at the
differences in intraday patterns. So I want to put them on a common 0-24h
scale and then do various kinds of plots and analyses, keeping the
conventional display form (10:30 etc.) when specific times display or
print. It looks as though chron:::times combined with trunc.POSIXt pretty
much solves my problem, except that `times` ignores the time units:
It uses hours/minutes/seconds for values 1 day and uses days and fractions
of a day otherwise.
For values and operations that it has not considered it falls back to
the internal
representation.
Most of your examples start to make sense once you realize this.
as.POSIXct('2009-3-23 12:23')-trunc(as.POSIXct('2009-3-23 12:23'),day)
Time difference of 12.38333 hours
times(as.POSIXct('2009-3-23 12:23')-trunc(as.POSIXct('2009-3-23
12:23'),day))
Time in days: seems to treat difftimes as raw numbers!!
[1] 12.38333
Obviously I can work around this, but shouldn't `times` give an error when
it encounters an object of unknown class rather than unsafely using its
internal representation? Of course, better still if `times` converted
correctly
In general, `times` has other inconsistent and peculiar behavior:
times(2) = Time in days: 2 Allows specifying multi-day periods, OK
times(1.5) = Time in days: 1.5 Allows specifying fractional multi-day
periods, OK
times(0.5) = 12:00:00 Inconsistent format compared to times(1.5)
times(18:00:00) + times(18:00:00) = Time in days: 1.5, OK
times(36:00:00) = error Why does it allow times(1.5) and
times(18:00:00) + times(18:00:00) to specify 1.5 days, but not 36 hours?
times(-0.5) = -0.5 Why doesn't it print Time in days: -0.5?
times(18:00:00)/times(1:00:00) = Time in days: 18 Incorrect
dimensions; meaningless result -- should be dimensionless
times(18:00:00) * times(10:00:00) = 07:30:00 Incorrect dimensions;
meaningless result.
sin(times(18:00:00)) = 16:21:34 Meaningless result -- should be error
It's nice that R has a class system, but if code ignores the class
There is an article on dates and times in R News 4/1.
Thanks for the pointer.
-s
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[R] Class for time of day?
What is the recommended class for time of day (independent of calendar date)? And what is the recommended way to get the time of day from a POSIXct object? (Not a string representation, but a computable representation.) I have looked in the man page for DateTimeClasses, in the Time Series Analysis Task View and in Spector's Data Manipulation book but haven't found these. Clearly I can create my own Time class and hack around with the internal representation of POSIXct, e.g. days - unclass(d)/(24*3600) days-floor(days) and write print.Time, `-.Time`, etc. etc. but I expect there is already a standard class or CRAN package. -s [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Class for time of day?
There is a times class in the chron package. Times are measured in fractions of a day so 1/24 is one hour. library(chron) dt - Sys.time() tt - times(format(dt, %H:%M:%S)) tt [1] 12:27:46 tt + 1/24 [1] 13:27:46 There is an article on dates and times in R News 4/1. On Wed, May 20, 2009 at 10:57 AM, Stavros Macrakis macra...@alum.mit.edu wrote: What is the recommended class for time of day (independent of calendar date)? And what is the recommended way to get the time of day from a POSIXct object? (Not a string representation, but a computable representation.) I have looked in the man page for DateTimeClasses, in the Time Series Analysis Task View and in Spector's Data Manipulation book but haven't found these. Clearly I can create my own Time class and hack around with the internal representation of POSIXct, e.g. days - unclass(d)/(24*3600) days-floor(days) and write print.Time, `-.Time`, etc. etc. but I expect there is already a standard class or CRAN package. -s [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Re: [R] Class for time of day?
If you want the hours from a POSIXct, here is one way of doing it; you can create a function for doing it: x - Sys.time() x [1] 2009-05-20 12:17:13 EDT y - difftime(x, trunc(x, units='days'), units='hours') y Time difference of 12.28697 hours as.numeric(y) [1] 12.28697 It depends on what type of computations you want to do with it. You can leave it as POSIXct and carry out a lot of them. Can you specify what you want? On Wed, May 20, 2009 at 10:57 AM, Stavros Macrakis macra...@alum.mit.eduwrote: What is the recommended class for time of day (independent of calendar date)? And what is the recommended way to get the time of day from a POSIXct object? (Not a string representation, but a computable representation.) I have looked in the man page for DateTimeClasses, in the Time Series Analysis Task View and in Spector's Data Manipulation book but haven't found these. Clearly I can create my own Time class and hack around with the internal representation of POSIXct, e.g. days - unclass(d)/(24*3600) days-floor(days) and write print.Time, `-.Time`, etc. etc. but I expect there is already a standard class or CRAN package. -s [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.htmlhttp://www.r-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. -- Jim Holtman Cincinnati, OH +1 513 646 9390 What is the problem that you are trying to solve? [[alternative HTML version deleted]] __ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
