Hi all, I have a simple data frame, first list is a list of dates (in
"%Y-%m-%d" format) and second list an observation on that particular
date. There might not be observations everyday. Let's just say
there are no observations on saturdays and sundays. Now I want to
select the first obs
Here is one way of doing it:
> x <- "DateObservation
+ 2007-05-23 20
+ 2007-05-22 30
+ 2007-05-21 10
+ 2007-04-10 50
+ 2007-04-09 40
+ 2007-04-07 30
+ 2007-03-05 10"
> x <- read.table(tex
Use the zoo package to represent data like this.
Here time(z) is a vector of the dates and as.yearmon(time(z))
is the year/month of each date. With FUN=head1, ave picks out the first
date in any month and aggregate then aggregates over all
values in the same year/month choosing the first one.
Li
I have only just able to dissect Jim's solution and realize I am
actually not very far away from the answer. One last step was to use
"lapply". Jim, thanks again for the help.
Gabor, thanks for the suggestion. Let me have a read on what the zoo
package is about. Thanks a lot for the poin
One additional simplification. If we use simplify = FALSE then
tapply won't simplify its answer to numeric and we can
avoid using as.Date in the last solution:
window(z, tapply(time(z), as.yearmon(time(z)), head, 1, simplify = FALSE))
On 5/27/07, Gabor Grothendieck <[EMAIL PROTECTED]> wrote:
>
Here is one additional solution, also using zoo. Using z from
the prior solution as.yearmon(time(z)) is, as before, the year/month
of each date and tapply(time(z), as.yearmon(time(z)), head, 1)
gets the first date within each month; however, tapply converts it
to numeric so we use as.Date to conve
