[R] aggregation of a zoo object

[Achim Zeileis]

On Tue, 29 May 2007 jessica.gervais at tudor.lu wrote:

> # then I want to do the sum per hour
>
> z_sum_per_hour <- aggregate(na.omit(z), function(x) as.POSIXct(trunc(x,
> "hour")),sum)
> Warning message:
> some methods for “zoo” objects do not work if the index entries in
> ‘order.by’ are not unique in: zoo(rval[i], x.index[i])
>
> Do anyone has an idea how to avoid that ?

The warning does not come from the aggregate() call, but from the
na.omit() call. After omitting the NAs, you have still duplicated time
stamps, hence the warning is issued again. After that, aggregating works
fine and produces no warnings.
Z