R help - Apr 2011 - Discretizing data rows into regular intervals

Hi guys,

I'd like to thank you ahead of time for any help that you can offer me.
I'm kind of stuck trying to do this.

I have a data frame with dates and values (note: only two columns shown):

head(test)
        date     value         stop
1     01/02/05     100     12/01/07
2     07/16/05     200     12/01/07
3     12/20/05     150     12/01/07
4     04/01/06     250     12/01/07
5     10/01/06      10     12/01/07

What I need to do is create regularly spaced 3-month intervals (starting
with the first observed date) with values that are closest to but recorded
after the date created. I would stop at the stop date. So the result would
look like:

      new_date   value
1     01/02/05     100
2     04/02/05     100
3     07/02/05     100
4     10/02/05     200
5     01/02/06     150
6     04/02/06     250
7     07/02/06     250
8     10/02/06      10
9     01/02/07      10
etc
etc
etc   10/02/07     ---  ## Final obs since next one would be 1/2/08 (after
stop date)

Again, I would be extremely grateful for any help.

Thanks,

-linh

The ?cut function should work for that. Have you tried?

D.

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Sorry, I did not get the question because I read it too sloppily. I hope this
is not homework. You can proceed along this example:

set.seed(32345)

#Value of observation
value=rpois(60,100)

#Day of observation
day=sample(1:1080,50,replace=F)
day=sort(day)

#Assume 3 years
#Assume months have all 30 days
#For real dates, the breaks in cut()
#have to be defined properly
all.days=seq(from=1,to=1080)
quarter=cut(all.days,breaks=12)
quarter=as.factor(as.numeric(quarter))

#In which quarter is a certain observation
quarter.of.day=quarter[day]

#What's the minimum day in a quarter
min.day=tapply(day,quarter.of.day,min)

#What's the value at that day
values.at.min.day=value[which(day%in%min.day)]

hth,
daniel

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On Sat, Apr 2, 2011 at 9:31 PM, Linh Tran <Tranlm at berkeley.edu>
wrote:
> Hi guys,
>
> I'd like to thank you ahead of time for any help that you can offer me.
> I'm kind of stuck trying to do this.
>
> I have a data frame with dates and values (note: only two columns shown):
>
> head(test)
> ? ? ? ?date ? ? value ? ? ? ? stop
> 1 ? ? 01/02/05 ? ? 100 ? ? 12/01/07
> 2 ? ? 07/16/05 ? ? 200 ? ? 12/01/07
> 3 ? ? 12/20/05 ? ? 150 ? ? 12/01/07
> 4 ? ? 04/01/06 ? ? 250 ? ? 12/01/07
> 5 ? ? 10/01/06 ? ? ?10 ? ? 12/01/07
>
> What I need to do is create regularly spaced 3-month intervals (starting
> with the first observed date) with values that are closest to but recorded
> after the date created. I would stop at the stop date. So the result would
> look like:
>
> ? ? ?new_date ? value
> 1 ? ? 01/02/05 ? ? 100
> 2 ? ? 04/02/05 ? ? 100
> 3 ? ? 07/02/05 ? ? 100
> 4 ? ? 10/02/05 ? ? 200
> 5 ? ? 01/02/06 ? ? 150
> 6 ? ? 04/02/06 ? ? 250
> 7 ? ? 07/02/06 ? ? 250
> 8 ? ? 10/02/06 ? ? ?10
> 9 ? ? 01/02/07 ? ? ?10
> etc
> etc
> etc ? 10/02/07 ? ? --- ?## Final obs since next one would be 1/2/08 (after
> stop date)
>
See question #13 in the zoo-faq vignette:
http://cran.r-project.org/web/packages/zoo/index.html
and note the existence of zoo's yearqtr class.

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