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]]


