Thanks Berend,

I don't know why I didn't try that before posting the question... but...
anyways, thanks for your help

Srecko


On Thu, Aug 29, 2013 at 11:34 AM, Berend Hasselman <bhh@xs4all.nl> wrote:

>
> On 29-08-2013, at 20:15, srecko joksimovic <sreckojoksimovic@gmail.com>
> wrote:
>
> > Thanks Arun,
> >
> > this is great. However, it should be just a little bit different:
> >
> > #  id  event       time time_on_task
> > #1  1    add 1373502892           80
> > #2  2    add 1373502972           23
> > #3  3 delete 1373502995           901
> > #4  4   view 1373503896          100
> > #5  5    add 1373503996          NA
> >
> > When I calculate difference, I need to know how long each activity was.
> It
> > is id2-id1 for the first activity...
>
> then why don't you try
>
> dat1$time_on_task<- c(diff(dat1$time),NA)
>
> Berend
>
>

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