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McClatchie, Sam (PIRSA-SARDI)

2005-Aug-15 07:27 UTC

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

Background:
OS: Linux Mandrake 10.1
release: R 2.0.0
editor: GNU Emacs 21.3.2
front-end: ESS 5.2.3
---------------------------------
Colleagues

I have a  wind speed time series with a normal frequency distribution and a
spike in the 5 metres/second bin. The most likely explanation is that the
instrument was returning duplicate values at this speed. To check  this, I
want to extract all the unique times from the series. However, unique()
works with vectors and the object is POSIXt class. I've looked for a similar
function to unique() that will work with this class, but have failed to find
one.

Any suggestions?

Thanks

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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Petr Pikal

2005-Aug-15 08:10 UTC

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

Hi Sam

It works for me:

ss<-Sys.time()
sss<-rep(ss,5)
ss<-Sys.time()
sss<-c(sss,ss)> sss[1] "2005-08-15 10:04:02 St??edn?? Evropa (letn?? ??as)"
"2005-08-15
10:04:02 St??edn?? Evropa (letn?? ??as)"
[3] "2005-08-15 10:04:02 St??edn?? Evropa (letn?? ??as)"
"2005-08-15
10:04:02 St??edn?? Evropa (letn?? ??as)"
[5] "2005-08-15 10:04:02 St??edn?? Evropa (letn?? ??as)"
"2005-08-15
10:04:35 St??edn?? Evropa (letn?? ??as)"

# six values but only 2 different
> unique(sss)[1] "2005-08-15 10:04:02 St??edn?? Evropa (letn?? ??as)"
"2005-08-15
10:04:35 St??edn?? Evropa (letn?? ??as)"

# 2 values
> str(sss)'POSIXct', format: chr [1:6] "2005-08-15 10:04:02"
"2005-08-15
10:04:02" "2005-08-15 10:04:02" "2005-08-15 10:04:02"
"2005-
08-15 10:04:02" ...

# posix format as well

HTH
Petr





On 15 Aug 2005 at 16:57, McClatchie, Sam (PIRSA-SARDI) wrote:
> Background:
> OS: Linux Mandrake 10.1
> release: R 2.0.0
> editor: GNU Emacs 21.3.2
> front-end: ESS 5.2.3
> ---------------------------------
> Colleagues
> 
> I have a  wind speed time series with a normal frequency distribution
> and a spike in the 5 metres/second bin. The most likely explanation is
> that the instrument was returning duplicate values at this speed. To
> check  this, I want to extract all the unique times from the series.
> However, unique() works with vectors and the object is POSIXt class.
> I've looked for a similar function to unique() that will work with
> this class, but have failed to find one.
> 
> Any suggestions?
> 
> Thanks
> 
> 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/>
> 
>                    /\
>       ...>><xX(??> 
>                 //// \\\\
>                    <??)Xx><<
>               /////  \\\\\\
>                         ><(((??> 
>   >><(((??>   ...>><xX(??>O<??)Xx><<
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
> http://www.R-project.org/posting-guide.html
Petr Pikal
petr.pikal at precheza.cz

Prof Brian Ripley

2005-Aug-15 08:39 UTC

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

On Mon, 15 Aug 2005, McClatchie, Sam (PIRSA-SARDI) wrote:
> Background:
> OS: Linux Mandrake 10.1
> release: R 2.0.0
Time for an update.
> editor: GNU Emacs 21.3.2
> front-end: ESS 5.2.3
> ---------------------------------
> Colleagues
>
> I have a  wind speed time series with a normal frequency distribution and a
> spike in the 5 metres/second bin. The most likely explanation is that the
> instrument was returning duplicate values at this speed. To check  this, I
> want to extract all the unique times from the series. However, unique()
> works with vectors and the object is POSIXt class. I've looked for a
similar
> function to unique() that will work with this class, but have failed to
find
> one.
foo[!duplicated(unclass(foo))]

works, for POSIXct (POSIXt is a virtual class covering that and POSIXlt: 
for the latter convert to POSIXct).

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

McClatchie, Sam (PIRSA-SARDI)

2005-Aug-16 01:37 UTC

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

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/>
  
                   /\
      ...>><xX(??> 
                //// \\\\
                   <??)Xx><<
              /////  \\\\\\
                        ><(((??> 
  >><(((??>   ...>><xX(??>O<??)Xx><<

Petr Pikal

2005-Aug-16 13:32 UTC

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

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