[R] zoo: hourly values (local time) not unique

[vwl-mailingliste at gmx.de]

Hi!

I've got a time series as a zoo object which contains hourly values. My problem is that these values occur in every "real" hour with regard to daylight savings time. I.e. the last sunday in march, i'll have 23values whereas the last sunday in october contains 25 values instead of 24. 
Thus if I try to aggregate the data using for example tapply (e.g. to get a monthly mean), I get the error 

"some methods for "zoo" objects do not work if the index entries in 'order.by' are not unique"

Any idea how I can solve this without having to remove/add an hour each year manually? Or, as I'm quite new to R, how I could easily manipulate my data so that the "missing" hour is introduced and the "double" hour is cut from the data (and the index)?

I'd really appreciate your help! Thanks in advance,
Arne
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