R help - May 2010 - Add 1 week to date with hours included for subset

Forum, 

I've got hourly data for roughly 5 months of time that I want to subset into
successive weeks.  The first two elements of the dataset are

well.80.2$date[1]
>[1] 6/12/2000 2:00
>9256 Levels: 10/1/2001...
well.80.2$date[2]
>[1] 6/12/2000 3:00
>9256 Levels: 10/1/2001....
and so on until mid-october.  I've been able to add 1 week the first element
with the following:

as.POSIXlt(paste(as.character(as.Date(well.80.2$date[1],"%m/%d/%Y
%H:%M")+7),as.character(format(strptime(well.80.2$date[1],"%m/%d/%Y
%H:%M"),"%H:%M")),sep=" "))
>[1] "2000-06-19 02:00:00"
  
What I've been unable to do is then use this for comparative purposes in the
subset command, something to the effect of:

contin.80.2<-subset(well.80.2,well.80.2$date>=well.80.2$date[1]) &
well.80.2$date <
as.POSIXlt(paste(as.character(as.Date(well.80.2$date[1],"%m/%d/%Y
%H:%M")+7),as.character(format(strptime(well.80.2$date[1],"%m/%d/%Y
%H:%M"),"%H:%M")),sep=" "))

If there is an easier way to parse the dataset into weekly bins taking into
consideration the hours, I'm open to suggestions.

Thank you.

-- 
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On May 13, 2010, at 11:25 PM, emorway wrote:
>
> Forum,
>
> I've got hourly data for roughly 5 months of time that I want to  
> subset into
> successive weeks.  The first two elements of the dataset are
>
> well.80.2$date[1]
>> [1] 6/12/2000 2:00
>> 9256 Levels: 10/1/2001...
>
> well.80.2$date[2]
>> [1] 6/12/2000 3:00
>> 9256 Levels: 10/1/2001....
>
> and so on until mid-october.  I've been able to add 1 week the first  
> element
> with the following:
>
> as.POSIXlt(paste(as.character(as.Date(well.80.2$date[1],"%m/%d/%Y
>
%H:%M")+7),as.character(format(strptime(well.80.2$date[1],"%m/%d/%Y
> %H:%M"),"%H:%M")),sep=" "))
>> [1] "2000-06-19 02:00:00"
>
> What I've been unable to do is then use this for comparative  
> purposes in the
> subset command, something to the effect of:
>
> contin.80.2<-subset(well.80.2,well.80.2$date>=well.80.2$date[1])
&
You simply cannot do comparisons with factor data. You need to make a  
variable that is of Date or DateTime or ti or zoo class. Then do you  
comparisons.
> well.80.2$date <
> as.POSIXlt(paste(as.character(as.Date(well.80.2$date[1],"%m/%d/%Y
>
%H:%M")+7),as.character(format(strptime(well.80.2$date[1],"%m/%d/%Y
> %H:%M"),"%H:%M")),sep=" "))
>
> If there is an easier way to parse the dataset into weekly bins  
> taking into
> consideration the hours, I'm open to suggestions.
>
> Thank you.
>
> -- 
-- 

David Winsemius, MD
West Hartford, CT

For those whose search lands on this post, here is the solution I found that
worked

well.80.2<-data.frame(well.80.2,week=floor(as.numeric(difftime(strptime(well.80.2$date,"%m/%d/%Y
%H:%M",tz=""),strptime(well.80.2$date[1],"%m/%d/%Y
%H:%M",tz=""),tz="",units="hours"))/168))

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