[R] aggregating data with Zoo

[Alfonso Sammassimo]

Thankyou Achim.

Along these lines, how might I extract subsets from that set by day of week?
eg: create a new series that includes Mondays only.

Thanks,
Alf
----- Original Message ----- 
From: "Achim Zeileis" <Achim.Zeileis at R-project.org>
To: "Alfonso Sammassimo" <cincinattikid at bigpond.com>
Cc: <r-help at stat.math.ethz.ch>
Sent: Thursday, March 29, 2007 1:16 AM
Subject: Re: [R] aggregating data with Zoo


> 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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>