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.
