[R] Re membering the last time an event occurred within a dataframe

[Gabor Grothendieck]

Try:

cumsum(myData$evid)


On Thu, Jul 3, 2008 at 2:19 PM, Jim Price <price_ja at hotmail.com> wrote:
>
> All,
>
> I am constructing a pharmacokinetic dataset and have hit a snag. The dataset
> can be demonstrated in the following way:
>
>
>
> myData <- data.frame(
>        evid = c(1, 0, 0, 0, 1, 0, 1, 1, 1, 0),
>        time = 1:10,
>        last.dose.time = c(1, 1, 1, 1, 5, 5, 7, 8, 9, 9)
> )
>
>
> The evid field is an indicator variable for whether the associated
> observation is a dosing record (when it takes value 1) or an observation
> (where it takes value 0). The time field is a date-time record for the
> associated dose / observation event. I'm trying to calculate the time since
> the last dose for each observation event - to support that, the data I'd
> like to end up with is contained in last.dose.time, which gives the time at
> which the last dosing event occured.
>
> The problem is in calculating the last.dose.time field; this is the first
> time I've done this particular kind of data manipulation in R and I just
> can't get my head around the code to solve it.
>
> I've been eyeballing rle and I think there may be a solution hiding in there
> somewhere, but I'm still failing to progress. Any help would be appreciated!
>
>
> Thanks in advance,
>
> Jim Price
> Cardiome Pharma. Corp.
>
> --
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>
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