[R] converting a time to nearest half-hour

[stephen sefick]

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
>
> ______________________________________________
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> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Stephen Sefick
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