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 <www...@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.liakhovit...@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
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