On Fri, Apr 2, 2010 at 10:49 AM, Doran, Harold <HDoran at air.org>
wrote:> I have not used POSIX classes previously and now have a need to use them. I
have sports data with times of some athletes
The main reason to use POSIXct is if you need time zones.
If you don't then you might be better off with chron. See R News 4/1.
> library(chron)
> tt <- times(c('00:14:15', '00:16:45'))
> summary(tt)
Min. 1st Qu. Median Mean 3rd Qu. Max.
00:14:15 00:14:52 00:15:30 00:15:30 00:16:08 00:16:45> min(tt); max(tt); mean(tt)
[1] 00:14:15
[1] 00:16:45
[1] 00:15:30
> rank(tt)
[1] 1 2> order(tt)
[1] 1 2> sort(tt)
[1] 00:14:15 00:16:45> tt[order(tt)]
[1] 00:14:15 00:16:45
> after different events. I need to perform some simple analyses using the
times. I think I've figured out how to do this. I just want to confirm with
others who have more experience that this is indeed the correct approach. If
not, please suggest a more appropriate way.
>
> Suppose I have times for two athletes after event 1.
>
>> times <- c('14:15', '16:45')
>
> Now, I use strptime() as follows
>
>> ?x <- strptime(times, "%M:%S")
>> x
> [1] "2010-04-02 00:14:15" "2010-04-02 00:16:45"
>
>> class(x)
> [1] "POSIXt" ?"POSIXlt"
>
> Now, I want the average time across all athletes as well as the min and
max, so I do:
>
>> mean(x); min(x); max(x)
> [1] "2010-04-02 00:15:30 EDT"
> [1] "2010-04-02 00:14:15 EDT"
> [1] "2010-04-02 00:16:45 EDT"
>
> Now, I want to rank order the athletes:
>
>> rank(x)
> Error in if (xi == xj) 0L else if (xi > xj) 1L else -1L :
> ?missing value where TRUE/FALSE needed
>
> But, I can rank order the following.
>
>> rank(times)
> [1] 1 2
>
> I don't need the date in the object x, but I can't figure out how
to remove it. Nonetheless, it doesn't seem to affect anything.
>
>> x
> [1] "2010-04-02 00:14:15" "2010-04-02 00:16:45"
>
> Is this the right approach for using time variables and performing some
computations on them? Or, is there another approach I should look at.
>
> Thanks,
> Harold
>
>> sessionInfo()
> R version 2.10.0 (2009-10-26)
> i386-pc-mingw32
>
> locale:
> [1] LC_COLLATE=English_United States.1252 ?LC_CTYPE=English_United
States.1252
> [3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C
> [5] LC_TIME=English_United States.1252
>
> attached base packages:
> [1] stats ? ? graphics ?grDevices utils ? ? datasets ?methods ? base
>
> other attached packages:
> [1] lme4_0.999375-32 ? Matrix_0.999375-31 lattice_0.17-26
>
> loaded via a namespace (and not attached):
> [1] grid_2.10.0 ?tools_2.10.0
>
> ? ? ? ?[[alternative HTML version deleted]]
>
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