I also find that POSIXct is generally the most useful, and only use POSIXlt in special cases.
But have you considered as.POSIXct() instead of strptime()? It works for me, and I can't remember the last time I had to use strptime() for converting character to date/time. (But I mostly don't work with multiple time zones, except for converting to/from UTC. -Don -- Don MacQueen Lawrence Livermore National Laboratory 7000 East Ave., L-627 Livermore, CA 94550 925-423-1062 On 3/29/12 12:11 PM, "Steven R Corsi" <srco...@usgs.gov> wrote: >Thanks for the link Michael. This is a very good explanation with some >very useful tips on which date classes to use for different purposes. It >generally strengthened the concept that POSIXct is the way to go unless >you need to extract specific components of the date from POSIXlt. Since >strptime() appears to be the primary conversion route from character >class with dates/times/time zones to a date/time class, and since >strptime() results in a POSIXlt format, that was what I was commonly >using in past applications. That format, at times, gave me errors in >situations where I didn't expect them. Now it is clear that the second >step of conversion to POSIXct is preferred for many purposes. > >Best Regards >Steve > >=============================================== >Steven R. Corsi Phone: (608) 821-3835 >Research Hydrologist email: srco...@usgs.gov >U.S. Geological Survey >Wisconsin Water Science Center >8505 Research Way >Middleton, WI 53562 >=============================================== > > >On 3/29/2012 1:28 PM, R. Michael Weylandt wrote: >> That's generally my reaction to them, but you should also read "R News >> 4/1 -- Help Desk" >> (http://cran.r-project.org/doc/Rnews/Rnews_2004-1.pdf) which gives >> some tips on Date()s and the various time classes. >> >> Best, Michael >> >> On Thu, Mar 29, 2012 at 2:19 PM, Steven R Corsi<srco...@usgs.gov> >>wrote: >>> Thanks very much for the response. That was a very good article and >>>gives me >>> a good appreciation for the history and covers the structure of the two >>> date/time formats well. >>> >>> What I was specifically looking for is a feel for the situations when >>>one >>> format should be used over the other. In my work, I have gotten the >>> impression that I should just use POSIXct for general useability in >>> functions and graphics until I need to extract specific date >>>components such >>> as month, day, year, etc. In those instances, just convert to POSIXlt >>>and >>> extract needed info. Is this mostly accurate? More generally, is there >>>a >>> resource that summarizes which date/time objects to use under which >>> conditions? So far, I have mostly been learning by trial/error/web >>>searching >>> which eventually is effective, but can be quite slow. >>> >>> Thanks >>> Steve >>> >>> =============================================== >>> Steven R. Corsi Phone: (608) 821-3835 >>> Research Hydrologist email: srco...@usgs.gov >>> U.S. Geological Survey >>> Wisconsin Water Science Center >>> 8505 Research Way >>> Middleton, WI 53562 >>> =============================================== >>> >>> >>> >>> On 3/28/2012 12:16 PM, Duncan Murdoch wrote: >>>> On 28/03/2012 10:06 AM, Steven R Corsi wrote: >>>>> Hello R users >>>>> >>>>> I am searching for a descriptive summary of the use of POSIXlt as >>>>> compared to POSIXct date/time formats. I have been using them >>>>> extensively for different purposes, but still can't quite understand >>>>> when to use which one for the most efficient coding and use. I >>>>>typically >>>>> use them in graphics, comparison of times, interpolation of values >>>>> between times, computation of time-series parameters, and so on. >>>>> >>>>> My request is simply to learn if there is a resource out there that >>>>> explains the strengths of the use of each format in different >>>>>situations >>>>> and if certain situations require one over the other. My web searches >>>>> have turned up basic things like the vector form (POSIXlt) vs the >>>>> decimal form (POSIXct), but I could not find specific guidance to >>>>> understand when it is best to use one over the other. >>>> >>>> The first of the "Other Topics" among the "Technical Papers" available >>>> from the main HTML help page in R should address this. >>>> >>>> Duncan Murdoch >>> >>> ______________________________________________ >>> 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. ______________________________________________ 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.
