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

From: McClatchie, Sam (PIRSA-SARDI) <mcclatchie.sam_at_saugov.sa.gov.au>
Date: Tue 16 Aug 2005 - 11:37:08 EST


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@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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