[R] return unique values from date/time class object

[McClatchie, Sam (PIRSA-SARDI)]

Background:
OS: Linux Mandrake 10.1
release: R 2.1.1
editor: GNU Emacs 21.3.2
front-end: ESS 5.2.3
---------------------------------

Thanks to Brian Ripley (I've upgraded from source, thanks for the reminder)
and Petr Pikal for their suggestions, but I have not made clear the form of
my data:

Browse[1]> ceduna[1:10,]
                  LSD AVIATION_ID WND_DIR WND_SPD_MPS
1  1/01/2001 10:30:00        YCDU     230         4.6
2  1/01/2001 11:00:00        YCDU     210         4.1
3  1/01/2001 11:30:00        YCDU     230         6.7
4  1/01/2001 12:00:00        YCDU     230         7.7
5  1/01/2001 12:30:00        YCDU     220         8.2
6  1/01/2001 13:00:00        YCDU     210         7.2
7  1/01/2001 13:30:00        YCDU     210         7.2
8  1/01/2001 14:00:00        YCDU     200         6.7
9  1/01/2001 14:30:00        YCDU     190         7.7
10 1/01/2001 15:00:00        YCDU     200         8.2
Browse[1]> class(ceduna)
[1] "data.frame"
Browse[1]>  x <- as.character(ceduna$LSD)
Browse[1]>     new.time <- strptime(x, "%d/%m/%Y %H:%M:%S")
Browse[1]> class(new.time)
[1] "POSIXt"  "POSIXlt"
Browse[1]> unique(new.time)
Error in unique.default(new.time) : unique() applies only to vectors
Browse[1]> tt <- new.time[!duplicated(unclass(new.time))]
Error in duplicated.default(unclass(new.time)) : 
	duplicated() applies only to vectors
Browse[1]> 

I'm obviously doing something silly with the data classes, but what?

Best fishes

Sam
----
Sam McClatchie,
Biological oceanography 
South Australian Aquatic Sciences Centre
PO Box 120, Henley Beach 5022
Adelaide, South Australia
email <mcclatchie.sam at saugov.sa.gov.au>
Cellular: 0431 304 497 
Telephone: (61-8) 8207 5448
FAX: (61-8) 8207 5481
Research home page <http://www.members.iinet.net.au/~s.mcclatchie/>
  
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