[R] Help with Time

[David Winsemius]

On Nov 21, 2014, at 3:19 PM, David Winsemius wrote:

> 
> On Nov 21, 2014, at 2:55 PM, Raghuraman Ramachandran wrote:
> 
>> Sorry I forgot to mention it clearly. I like to round it to the
>> nearest 30th minute that is past. So 12:28:59 will be again 12:00:00
>> and
>> 12:59:59 will be 12:30:00 etc. Apologies for the lack of clarity in
>> the beginning.
>> 
> 
> That's just truncation. Should be very easy to hack trunc.POSIXt to deliver that result. Add a "half_hr" unit to the list and then a simple extra clause that check for minutes >30.

In my first effort I used an if(){}else{} construction, committing the newbie mistake of forgetting it was not the vectoRized way. So this performs better:

trunc.POSIXt <- 
function (x, units = c("secs", "mins", "half_hrs", "hours", "days"), ...) 
{
    units <- match.arg(units)
    x <- as.POSIXlt(x)
    if (length(x$sec)) 
        switch(units, secs = {
            x$sec <- trunc(x$sec)
        }, mins = {
            x$sec[] <- 0
        }, half_hrs = { 
            x$sec[] <- 0
            x$min[] <- 0L+ 30L*(x$min >=30)
        }, hours = {
            x$sec[] <- 0
            x$min[] <- 0L
        }, days = {
            x$sec[] <- 0
            x$min[] <- 0L
            x$hour[] <- 0L
            x$isdst[] <- -1L
        })
    x
}

> time <- seq(Sys.time(), Sys.time()+60*120, by= 60*5)
> trunc(time, "half_hrs")
 [1] "2014-11-21 15:30:00 PST" "2014-11-21 15:30:00 PST"
 [3] "2014-11-21 15:30:00 PST" "2014-11-21 15:30:00 PST"
 [5] "2014-11-21 15:30:00 PST" "2014-11-21 15:30:00 PST"
 [7] "2014-11-21 16:00:00 PST" "2014-11-21 16:00:00 PST"
 [9] "2014-11-21 16:00:00 PST" "2014-11-21 16:00:00 PST"
[11] "2014-11-21 16:00:00 PST" "2014-11-21 16:00:00 PST"
[13] "2014-11-21 16:30:00 PST" "2014-11-21 16:30:00 PST"
[15] "2014-11-21 16:30:00 PST" "2014-11-21 16:30:00 PST"
[17] "2014-11-21 16:30:00 PST" "2014-11-21 16:30:00 PST"
[19] "2014-11-21 17:00:00 PST" "2014-11-21 17:00:00 PST"
[21] "2014-11-21 17:00:00 PST" "2014-11-21 17:00:00 PST"
[23] "2014-11-21 17:00:00 PST" "2014-11-21 17:00:00 PST"
[25] "2014-11-21 17:30:00 PST"


> -- 
> David.
> 
> 
>> Many thanks
>> Raghu
>> 
>> On Fri, Nov 21, 2014 at 10:52 PM, Raghuraman Ramachandran
>> <optionsraghu at gmail.com> wrote:
>>> Dear guRus
>>> 
>>> How can I round of time in R to the nearest 30th minute please?
>>> 
>>> For example suppose if
>>>> Sys.time()
>>> [1] "2014-11-21 22:49:05.59042 GMT"
>>> then I would like a function that outputs 22:30:00.
>>> 
>>> if Sys.time is 12:13:22 then I would like to get 12:00:00 etc.
>>> 
>>> Any help would be appreciated.
>>> 
>>> Many thanks and regards,
>>> Raghu
>> 
>> __________________________________

> 

David Winsemius
Alameda, CA, USA