Re: [Rd] manipulating the Date Time classes
try xts package and functions: reclass period.max period.min best, daniel 2011/2/8 Mike Williamson this.is@gmail.com Hello, This is mostly to developers, but in case I missed something in my literature search, I am sending this to the broader audience. - Are there any plans in the works to make time classes a bit more friendly to the rest of the R world? I am not suggesting to allow for fancy functions to manipulate times, per se, or to figure out how to properly add times or anything complicated. Just some fixes to make it easier to work with the time classes. Here is a sampling of some strange bugs with the time classes that, to my knowledge, don't exist with any other core classes: 1. you cannot unlist a time without losing the class. E.g., if you unlist 2010-12-14 20:25:40 (POSIXct), you get 1292387141, at least on my OS with my time zone. Regardless of the exact number, unlisting a time class converts it to a numeric. - upon converting to a numeric, it seems there is an underlying, assumed origin of 1970-01-01 00:00:00. However, this same assumption does not underlie the conversion *back* to a POSIX time, e.g., through as.POSIXct() function. Therefore, whenever a time is accidentally converted to a numeric, I have to force it back to a time through as.POSIXct(), *providing my own details* as to the origin. There is no easy way to find the underlying origin. This makes me nervous for any persistent functions I create. If the underlying origin ever changes, then all this code will be inaccurate. Maybe the origin will never change, but regardless it makes more sense to allow for the same underlying origin default for as.POSIXct that is used when unlisting, or similar activities that force the time into a numeric. 2. you cannot perform functions that otherwise seem trivial, such as a max or min. I understand why, for instance, adding is hard. But what about max or min? Greater than or less than are possible, as is order(). I have my own simple scripts using these 2 functions in order to create a max min for times, but it would be nice to have something vetted official. If others could chime in with any strange behaviors they've seen in working with times, maybe we could get a critical mass of issues that are worthy of an overhaul. Thanks Regards, Mike Telescopes and bathyscaphes and sonar probes of Scottish lakes, Tacoma Narrows bridge collapse explained with abstract phase-space maps, Some x-ray slides, a music score, Minard's Napoleanic war: The most exciting frontier is charting what's already here. -- xkcd -- Help protect Wikipedia. Donate now: http://wikimediafoundation.org/wiki/Support_Wikipedia/en [[alternative HTML version deleted]] __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel [[alternative HTML version deleted]] __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
Re: [Rd] manipulating the Date Time classes
Firstly, don't double post. On Tue, Feb 8, 2011 at 2:24 PM, Mike Williamson this.is@gmail.com wrote: Hello, This is mostly to developers, but in case I missed something in my literature search, I am sending this to the broader audience. - Are there any plans in the works to make time classes a bit more friendly to the rest of the R world? I am not suggesting to allow for fancy functions to manipulate times, per se, or to figure out how to properly add times or anything complicated. Just some fixes to make it easier to work with the time classes. Here is a sampling of some strange bugs with the time classes that, to my knowledge, don't exist with any other core classes: 1. you cannot unlist a time without losing the class. E.g., if you unlist 2010-12-14 20:25:40 (POSIXct), you get 1292387141, at least on my OS with my time zone. Regardless of the exact number, unlisting a time class converts it to a numeric. You didn't say what your OS is, but two things spring to mind. Why are you calling 'unlist' on an object that isn't a list and ... it works for me: unlist(Sys.time()) [1] 2011-02-08 14:46:24.262146 CST - upon converting to a numeric, it seems there is an underlying, assumed origin of 1970-01-01 00:00:00. However, this same assumption does not underlie the conversion *back* to a POSIX time, e.g., through as.POSIXct() function. Therefore, whenever a time is accidentally converted to a numeric, I have to force it back to a time through as.POSIXct(), *providing my own details* as to the origin. There is no easy way to find the underlying origin. This makes me nervous for any persistent functions I create. If the underlying origin ever changes, then all this code will be inaccurate. Maybe the origin will never change, but regardless it makes more sense to allow for the same underlying origin default for as.POSIXct that is used when unlisting, or similar activities that force the time into a numeric. If it is just numeric, it shouldn't have any attribute and since the origin isn't global, you're sort of stuck. You can keep track of it yourself, or just leave it as the standard unix epoch. 2. you cannot perform functions that otherwise seem trivial, such as a max or min. I understand why, for instance, adding is hard. But what about max or min? Greater than or less than are possible, as is order(). I have my own simple scripts using these 2 functions in order to create a max min for times, but it would be nice to have something vetted official. min(Sys.time()+1:10) [1] 2011-02-08 14:59:26.40236 CST max(Sys.time()+1:10) [1] 2011-02-08 14:59:36.762224 CST Again, works for me. R.version _ platform x86_64-apple-darwin10.2.0 arch x86_64 os darwin10.2.0 system x86_64, darwin10.2.0 status major 2 minor 12.0 year 2010 month 10 day15 svn rev53317 language R version.string R version 2.12.0 (2010-10-15) If others could chime in with any strange behaviors they've seen in working with times, maybe we could get a critical mass of issues that are worthy of an overhaul. Thanks Regards, Mike Telescopes and bathyscaphes and sonar probes of Scottish lakes, Tacoma Narrows bridge collapse explained with abstract phase-space maps, Some x-ray slides, a music score, Minard's Napoleanic war: The most exciting frontier is charting what's already here. -- xkcd -- Help protect Wikipedia. Donate now: http://wikimediafoundation.org/wiki/Support_Wikipedia/en [[alternative HTML version deleted]] __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel -- Jeffrey Ryan jeffrey.r...@lemnica.com www.lemnica.com __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
Re: [Rd] manipulating the Date Time classes
Mike, On Feb 8, 2011, at 3:24 PM, Mike Williamson wrote: Hello, This is mostly to developers, but in case I missed something in my literature search, I am sending this to the broader audience. - Are there any plans in the works to make time classes a bit more friendly to the rest of the R world? I am not suggesting to allow for fancy functions to manipulate times, per se, or to figure out how to properly add times or anything complicated. Just some fixes to make it easier to work with the time classes. Here is a sampling of some strange bugs with the time classes that, to my knowledge, don't exist with any other core classes: 1. you cannot unlist a time without losing the class. E.g., if you unlist 2010-12-14 20:25:40 (POSIXct), you get 1292387141, at least on my OS with my time zone. Regardless of the exact number, unlisting a time class converts it to a numeric. Same answer as Jeff said - it works for me. When posting claims like this it's good to provide some evidence like a reproducible example with details such as the version of R you used, OS etc. - upon converting to a numeric, it seems there is an underlying, assumed origin of 1970-01-01 00:00:00. You may want to read up on times a bit - POSIX time (aka unix time) *is* defined as number of seconds elapsed since midnight UTC 1970/1/1. That is also the internal representation of POSIXct (see ?POSIXct) that you get when unclassing it (not unlisting). However, this same assumption does not underlie the conversion *back* to a POSIX time, e.g., through as.POSIXct() function. And it would be fatal if it did. When you have a number there is no way of knowing what the origin is, that's why it has to be specified. There are many different numeric times with various origins (e.g. Apple used to have its own one before OS X, Excel uses 1900 etc. - see Epoch). Therefore, whenever a time is accidentally converted to a numeric, I have to force it back to a time through as.POSIXct(), *providing my own details* as to the origin. There is no easy way to find the underlying origin. In general, there is no way. *If* your numbers come from unclassing POSIXct then you can simply set the class back - which avoid other hassles such as the fact that you have no idea about the target time zone of the original number otherwise. This makes me nervous for any persistent functions I create. If the underlying origin ever changes, then all this code will be inaccurate. POSIX time is POSIX time (aka unix time) - that's where the name comes from! If that definition changes, we'll see more issues than your code ;). Maybe the origin will never change, but regardless it makes more sense to allow for the same underlying origin default for as.POSIXct that is used when unlisting, or similar activities that force the time into a numeric. 2. you cannot perform functions that otherwise seem trivial, such as a max or min. Again, I don't believe you: x = Sys.time() + 1:10 min(x) [1] 2011-02-08 17:17:47 EST max(x) [1] 2011-02-08 17:17:56 EST max(x) - min(x) Time difference of 9 secs I understand why, for instance, adding is hard. But what about max or min? Greater than or less than are possible, as is order(). I have my own simple scripts using these 2 functions in order to create a max min for times, but it would be nice to have something vetted official. If others could chime in with any strange behaviors they've seen in working with times, maybe we could get a critical mass of issues that are worthy of an overhaul. Please do provide some real evidence, like reproducible examples. So far none of your claims was verifiable. Cheers, Simon Thanks Regards, Mike Telescopes and bathyscaphes and sonar probes of Scottish lakes, Tacoma Narrows bridge collapse explained with abstract phase-space maps, Some x-ray slides, a music score, Minard's Napoleanic war: The most exciting frontier is charting what's already here. -- xkcd -- Help protect Wikipedia. Donate now: http://wikimediafoundation.org/wiki/Support_Wikipedia/en [[alternative HTML version deleted]] __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
