[R] aggregating data with Zoo

[Achim Zeileis]

On Wed, 28 Mar 2007, Alfonso Sammassimo wrote:

> Is there a way of aggregating 'zoo' daily data according to day of week? eg
> all Thursdays

Sure, the easiest way will probably differ depending on the time stamp 
class. One example might be this:
   ## small example with Date index
   z <- read.zoo(file.path(.find.package("zoo"), "doc", "demo1.txt"),
                 sep = "|", format = "%d %b %Y")
   ## visualization
   plot(z)
   ## aggregate along week days (via POSIXlt representation)
   aggregate(z, as.POSIXlt(time(z))$wday, mean)

hth,
Z

> I came across the 'nextfri' function in the documentation but am unsure how
> to change this so any day of week can be aggregated.
>
> I have used POSIX to arrange the data (not as 'zoo' series) according to day
> of week, but am curious if I've missed if a similar option available with
> zoo.
>
> Thank you for any help,
>
> Alf Sammassimo
> Melbourne, Australia
>
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