Thanks Stephen and Gabor. The zoo package is what I was looking for.

On Fri, Oct 3, 2008 at 5:44 PM, Gabor Grothendieck
<ggrothendieck@gmail.com>wrote:

> Check out the zoo package and its three vignettes and
> ?aggregate.zoo in particular.
>
> Also have a look at the article on dates and times in R News 4/1
> and note the chron class which, in fact, accepts inputs in the
> very form you have.
>
> On Fri, Oct 3, 2008 at 7:39 PM, Joe Kaser <jmkaser@gmail.com> wrote:
> > Hi and thanks in advance,
> >
> > I am fairly new with R so I hope this problem isn't too amateur.
> >
> > I have a vector of count data which correspond to vectors of date
> (%m/%d/%Y)
> > and time of day (%H:%M:%S).
> > I am trying to compute various statistics (e.g. daily max) by lumping the
> > data together by day.   I have been able to utilize tapply() and group
> the
> > counts together, but with the method I use I end up losing the
> corresponding
> > time of day information.
> >
> > This is what I have done so far
> >
> > data=*vector of integers
> > *hours= *"character" vector of times %H:%M:S% *
> > days= *"character" vector of dates %m/%d/%Y
> > *
> > hr.days=paste(days,hours)
> > hr.dayslt=as.POSIXlt(strptime(hr.days, format="%m/%d/%Y %H:%M:%S"))
> >
> > tapply(data,hr.dayslt$yday,max)
> >
> > This works to give me the counts I want corresponding to a Julain day,
> but
> > it does not tell me which hour corresponds to each daily maximum.  Is
> > tapply() the wrong route?
> >
> > Joe
> > *
> >
> >
> > *
> >
> >        [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
>

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