[R] summing values by week - based on daily dates - but with some dates missing

[David Winsemius]

On Mar 30, 2011, at 2:35 PM, Dimitri Liakhovitski wrote:

> Henrique, this is great, thank you!
>
> It's almost what I was looking for! Only one small thing - it doesn't
> "merge" the results for weeks that "straddle" 2 years. In my example -
> last week of year 2008 and the very first week of 2009 are one week.
> Any way to "join them"?
> Asking because in reality I'll have many years and hundreds of groups
> - hence, it'll be hard to do it manually.
>
>
> BTW - does format(dates,"%Y.%W") always consider weeks as starting  
> with Mondays?

see:

?strptime   # or maybe not.

(I initially tried format.Date and DateTimeClasses before finding the  
answer , i.e. that Mondays are the "start" for "%W" but that Sundays  
are the start for "%w", however for that "start" they go from 0 to 6,  
as they do for the wday component of POSIXlt as described on the  
DateTimeClasses page. The help page for format.Date does say to took  
at strptime, and I missed that paragraph the first time through  
because I have a typically fulfilled expectation that the help pages  
will have working "htmlish" links to such essential information. And I  
see on reading further that the link I offered may not work if you are  
on Windows.)


>
> Thank you very much!
> Dimitri
>
>
> On Wed, Mar 30, 2011 at 2:55 PM, Henrique Dallazuanna <wwwhsd at gmail.com 
> > wrote:
>> Try this:
>>
>> aggregate(value ~ group + format(dates, "%Y.%W"), myframe, FUN = sum)
>>
>>
>> On Wed, Mar 30, 2011 at 11:23 AM, Dimitri Liakhovitski
>> <dimitri.liakhovitski at gmail.com> wrote:
>>> Dear everybody,
>>>
>>> I have the following challenge. I have a data set with 2 subgroups,
>>> dates (days), and corresponding values (see example code below).
>>> Within each subgroup: I need to aggregate (sum) the values by week -
>>> for weeks that start on a Monday (for example, 2008-12-29 was a
>>> Monday).
>>> I find it difficult because I have missing dates in my data - so  
>>> that
>>> sometimes I don't even have the date for some Mondays. So, I can't
>>> write a proper loop.
>>> I want my output to look something like this:
>>> group   dates   value
>>> group.1 2008-12-29  3.0937
>>> group.1 2009-01-05  3.8833
>>> group.1 2009-01-12  1.362
>>> ...
>>> group.2 2008-12-29  2.250
>>> group.2 2009-01-05  1.4057
>>> group.2 2009-01-12  3.4411
>>> ...
>>>
>>> Thanks a lot for your suggestions! The code is below:
>>> Dimitri
>>>
>>> ### Creating example data set:
>>> mydates<-rep(seq(as.Date("2008-12-29"), length = 43, by = "day"),2)
>>> myfactor<-c(rep("group.1",43),rep("group.2",43))
>>> set.seed(123)
>>> myvalues<-runif(86,0,1)
>>> myframe<-data.frame(dates=mydates,group=myfactor,value=myvalues)
>>> (myframe)
>>> dim(myframe)
>>>
>>> ## Removing same rows (dates) unsystematically:
>>> set.seed(123)
>>> removed.group1<-sample(1:43,size=11,replace=F)
>>> set.seed(456)
>>> removed.group2<-sample(44:86,size=11,replace=F)
>>> to.remove<-c(removed.group1,removed.group2);length(to.remove)
>>> to.remove<-to.remove[order(to.remove)]
>>> myframe<-myframe[-to.remove,]
>>> (myframe)
>>>

David Winsemius, MD
Heritage Laboratories
West Hartford, CT