[R] converting a time to nearest half-hour

[Jeff Newmiller]

This truncates to quarter-hour rather than rounding to half-hour.

"stephen sefick" <ssefick at gmail.com> wrote:

>If you have a zoo series this should work.  If it doesn't then please
>tell me because I think it works.
>
>snap2min <- function(zoo, min="00:15:00"){
>min15 <- times(min)
>a <- aggregate(zoo, trunc(time(zoo), min15), function(x) mean(x, na.rm=TRUE))
>}
>
>hth
>
>Stephen Sefick
>
>On Fri, Jul 23, 2010 at 11:00 AM, David Winsemius
><dwinsemius at comcast.net> wrote:
>>
>> On Jul 23, 2010, at 11:35 AM, David Winsemius wrote:
>>
>>>
>>> On Jul 23, 2010, at 11:20 AM, <Murali.Menon at avivainvestors.com>
>>> <Murali.Menon at avivainvestors.com> wrote:
>>>
>>>> Hi folks,
>>>>
>>>> I've got a POSIXct datum as follows:
>>>>
>>>>> Sys.time()
>>>>
>>>> [1] "2010-07-23 11:29:59 BST"
>>>>
>>>> I want to convert this to the nearest half-hour, i.e., to "2010-07-23
>>>> 11:30:00 BST"
>>>>
>>>> (If the time were "11:59:ss", I want to convert to "12:00:00").
>>>>
>>>> How to achieve this?
>>>
>>> Couldn't you just coerce to numeric, divide by 60(sec)*30(half-hour
>>> minutes), round to integer, multiply by 60*30,  coerce to POSIXct?
>>
>> When I tried my method I see that one also needs to add or subtract the
>> proper number of seconds from Universal Time to get the output formatting
>> correct. (Probably demonstrates that I do not have the proper understanding
>> of the right place to employ a TZ specification.).
>>
>> David Winsemius, MD
>> West Hartford, CT
>>
>> ______________________________________________
>> R-help at 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.
>>
>
>
>
>-- 
>Stephen Sefick
>____________________________________
>| Auburn University                                   |
>| Department of Biological Sciences           |
>| 331 Funchess Hall                                  |
>| Auburn, Alabama                                   |
>| 36849                                                    |
>|___________________________________|
>| sas0025 at auburn.edu                             |
>| http://www.auburn.edu/~sas0025             |
>|___________________________________|
>
>Let's not spend our time and resources thinking about things that are
>so little or so large that all they really do for us is puff us up and
>make us feel like gods.  We are mammals, and have not exhausted the
>annoying little problems of being mammals.
>
>                                -K. Mullis
>
>______________________________________________
>R-help at 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.

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