> Does anybody know why get I this kind of strange situation:
> 
> Browse[2]> hcEnd
> [1] "2009-03-29 06:30:00"
> Browse[2]> class(hcEnd)
> [1] "POSIXlt" "POSIXt" 
> Browse[2]> is.na(hcEnd)
> [1] TRUE

pp<-as.POSIXlt("2009-03-29 06:30:00")
pp
[1] "2009-03-29 06:30:00"
class(pp)
[1] "POSIXlt" "POSIXt" 
is.na(pp)
[1] FALSE

So we can't repeat your example.

-- 
Curt Seeliger, Data Ranger
Raytheon Information Services - Contractor to ORD
seeliger.curt@epa.gov
541/754-4638



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