Try this:
tapply(starttime,list(submitdate, surveyor),min)
On Wed, Jun 10, 2009 at 4:20 PM, christiaan pauw <cjp...@gmail.com> wrote:
> Hi everyone
> I want to apply a function by two indices.
>
> I have a number of surveyors submitting questionnaires. I want to check the
> time of the first submission for the day for each surveyor and also see a
> NA is no submission was done on a particular day.
>
> This generates a sample of the data:
>
> starttime=c("11:07:32","14:07:28","11:32:21","13:27:49","11:45:05",
>
> "12:30:06","10:27:07","10:18:07","15:29:36","16:29:23","13:46:45","10:45:26"
> ,"09:21:14","10:29:51","12:32:56","11:06:02","12:41:36","11:03:47",
> "10:58:12","10:05:54")
>
> submitdate=c("2009-05-21","2009-06-02", "2009-05-12" ,"2009-05-21",
> "2009-05-21", "2009-05-07", "2009-05-19" ,"2009-05-13" ,"2009-06-05",
>
> "2009-05-13", "2009-06-05", "2009-05-28", "2009-05-15", "2009-05-28",
> "2009-06-05", "2009-05-28", "2009-05-12", "2009-05-28",
>
> "2009-05-07", "2009-05-20")
>
> surveyor=rep(LETTERS[1:4],5)
>
> data=data.frame(surveyor, submitdate,starttime)
>
>
> I can generate a list of the earliest submission per day:
>
> tapply(starttime,submitdate,min)
>
> or of the earliest submission per surveyor:
>
> tapply(starttime,surveyor,min)
>
> or of the number of submissions per surveyor day:
>
> table(submitdate,surveyor)
>
>
> But what I want is the time of the earliest submission per surveyor per day
> (and NA's where applicable)
>
>
> Can anyone offer some advice
>
> Thanks
>
> Christiaan
>
> [[alternative HTML version deleted]]
>
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>
--
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O
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