[R] aggregating values at discreet irregular time intervals into hourly values

[Gabor Grothendieck]

Try this:

library(tseries)

# create 3 hours of test data
set.seed(123)
st <- as.POSIXct("2008-12-19 19:11:03")
tt <- seq(from = st, to = st + 60 * 60 * 3, by = "min")
x <- irts(tt, sample(0:1, length(tt), replace = TRUE))

library(zoo)

# convert to zoo and chron
z <- zoo(coredata(x), as.chron(format(time(x))))

# add half hour to each time and then truncate to the hour
# aggregating over that
z.ag <- aggregate(z,
	trunc(time(z) + as.numeric(times("00:30:00")), "01:00:00"),
	sum)
z.ag

which gives:

> z.ag
(12/19/08 19:00:00) (12/19/08 20:00:00) (12/19/08 21:00:00) (12/19/08 22:00:00)
                 10                  28                  32                  17

Read the three vignettes (pdf documents) that come with zoo, see ?aggregate.zoo
in particular and see R News 4/1 for dates and times.


On Tue, Aug 18, 2009 at 4:45 PM, Mathieu Beaulieu<beam09 at hotmail.com> wrote:
>
> Hello R users,
>
> I'm a newby to R (and programming software at large) and I would need some help to sum up event data at discreet time and irregular time interval into a hourly frequency.
>
> Here is an example of my time series frame (irregular time-serie object - irts in the tseries package):
>
> time                        value
> 2008-12-19 19:11:03 GMT    1
> 2008-12-19 19:12:00 GMT     0
> 2008-12-19 19:42:39 GMT     1
> 2008-12-19 20:42:41 GMT     1
> 2008-12-19 20:42:45 GMT     1
> 2008-12-19 20:42:48 GMT     1
> 2008-12-19 20:42:55 GMT     1
> 2008-12-19 20:42:57 GMT     1
> 2008-12-19 20:43:07 GMT     1
> 2008-12-19 20:43:16 GMT     1
> 2008-12-19 21:05:45 GMT     1
> 2008-12-19 21:07:58 GMT     1
> 2008-12-19 22:08:00 GMT     1
> 2008-12-19 22:08:33 GMT     1
> 2008-12-19 23:09:58 GMT     1
> 2008-12-19 23:10:32 GMT     1
> 2008-12-19 23:13:00 GMT     0
> 2008-12-19 23:14:29 GMT     1
> 2008-12-19 23:14:32 GMT     1
> 2008-12-19 23:14:35 GMT     1
> 2008-12-19 23:30:35 GMT     1
> 2008-12-19 23:38:56 GMT     1
> 2008-12-19 23:44:00 GMT     0
> 2008-12-19 23:45:00 GMT     0
> 2008-12-20 00:46:00 GMT     1
> [...]
> 2009-05-13 13:45:36 GMT    1
>
> And i'm trying to obtain a regularly spaced time series object which would aggregates the events (value ==1) occuring 30 minutes before and after every hour into a hourly rate, a little bite like this:
>
> time                        value
> 2008-12-19 18:00:00 GMT    0
> 2008-12-19 19:00:00 GMT     1
> 2008-12-19 20:00:00 GMT     1
> 2008-12-19 21:00:00 GMT     9
> 2008-12-19 22:00:00 GMT     2
> 2008-12-19 23:00:00 GMT     5
> 2008-12-20 00:00:00 GMT     2
> 2008-12-20 01:00:00 GMT    1
> [...]
> 2009-05-13 13:00:00 GMT    0
> 2009-05-13 14:00:00 GMT    1
>
> So far, I've created a regular ts object (destination object I guess) based on my irregular one:
>
> Code example (not to be run):
> test.ts<-approx.irts(test.irts,seq(from=test.irts$time[1],
> to=test.irts$time[length(test.irts$time)],by = "1 hour"),rule=2,method="linear")
>
> Which creates the regular ts fine, but doesn't aggregate the events.
>
> I've tried to mess around with the aggregate function - but I can't get the codes right to do what I want. Here are examples of unsuccessful attempts:
>
> try = aggregate(test.irts$value, by= list(time=test.ts$time), FUN= mean)
> ERROR MESS: Error in FUN(X[[1L]], ...) : arguments must have same length
>
> try = aggregate.ts(test.irts$value,frequency(test.ts$time),nfrequency=1, ndeltat=1)
> PROBLEM: gives me only one vector for my values (no time vector) but they are NOT aggregated by hour.
>
> try = list(x=test.ts$time, y=aggregate.ts(test.irts$value, nfrequency=1))
> PROBLEM: Gives 2 separate vectors :hourly time step and values - but again, values are not aggregated by hour.
>
>
> I would appreciate any cue or help. Thank you
>
>
>
>
> Mathieu Beaulieu,
> Soil, Water & Environment Laboratory
> Institute for Resources, Environment and Sustainability
> University of British-Columbia
> 429-2202 Main Mall,
> Vancouver, BC,
> V6T 1Z4
> Canada
> http://www.landfood.ubc.ca/swel/
>
>
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