Re: [R] 15-min mean values

From: Gabor Grothendieck <ggrothendieck_at_gmail.com>
Date: Thu 02 Feb 2006 - 17:44:18 EST

Assume VDATE is a character vector. If its a factor first convert it using

        VDATE <- as.character(VDATE)

Lets assume we only need the times portion and later we handle the full case which may or may be needed.

We create a times object from the times portion of vdate and then in the aggregate statement we use trunc.times -- note that trunc.times is a recent addition to the chron package so make sure you have the latest chron and R 2.2.1. See ?trunc.times

# test data
library(chron)
library(zoo)
VDATE <- c("1998-10-22:02:11", "1998-10-22:02:12", "1998-10-22:02:13", "1998-10-22:02:14", "1998-10-22:02:15") WS <- c(12.5, 10.1, 11.2, 10.5, 11.5)

# convert VDATES to times class and aggregate vtimes <- times(sub(".*:(..:..)", "\\1:00", VDATE)) aggregate(zoo(WS), trunc(vtimes, "00:15:00"), mean)

If we need the day part too then its only a little harder.

Represent VDATE as a chron object, vdate. We do this by extracting out the date and time portions and converting each separately. We use regular expressions to do that conversion but show in a comment how to do it without regular expressions. See R News 4/1 Help Desk for more info on this and the table at the end of the article in particular.

# alternative way to convert to vdate would be:
# vdate <- chron(dates = as.numeric(as.Date(substring(VDATE, 1, 10))),
#	       times = paste(substring(VDATE, 12), 0, sep =":"))


vdate <- chron(dates = sub("(....)-(..)-(..).*", "\\2/\\3/\\1", VDATE),
	times = sub(".*:(..:..)", "\\1:00", VDATE))
aggregate(zoo(WS), chron(trunc(times(vdate), "00:15:00")), mean)

On 2/2/06, Augusto.Sanabria@ga.gov.au <Augusto.Sanabria@ga.gov.au> wrote:
>
> Good day everyone,
>
> I want to use zoo(aggregate) to calculate
> 15-min mean values from a wind dataset which
> has 1-min values. The data I have looks like this:
>
> vector VDATE vector WS
> 1 1998-10-22:02:11 12.5
> 2 1998-10-22:02:12 10.1
> 3 1998-10-22:02:13 11.2
> 4 1998-10-22:02:14 10.5
> 5 1998-10-22:02:15 11.5
> .
> .
> .
> n 2005-06-30:23:59 9.1
>
>
> I want to use:
>
> aggregate(zoo(WS),'in 15-min intervals',mean)
>
> How do you specify 'in 15-min intervals' using
> vector VDATE? The length of VDATE cannot be
> changed, otherwise it would be a trivial problem
> because I can generate a 15-min spaced vector
> using 'seq'.
>
> Am I missing something?
>
> Thanks a lot,
>
> Augusto
>
>
> --------------------------------------------
> Augusto Sanabria. MSc, PhD.
> Mathematical Modeller
> Risk Research Group
> Geospatial & Earth Monitoring Division
> Geoscience Australia (www.ga.gov.au)
> Cnr. Jerrabomberra Av. & Hindmarsh Dr.
> Symonston ACT 2609
> Ph. (02) 6249-9155
>
> ______________________________________________
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> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
>



R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Thu Feb 02 17:53:42 2006

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