[R] POSIXlt vs POSIXct

R. Michael Weylandt michael.weylandt at gmail.com
Thu Mar 29 20:28:34 CEST 2012

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 <srcorsi at 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: srcorsi at 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
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