R how to identify distance of last occurrence

Question

I want to calculate how long its been since something occurred.

Given the following, you can see that the light is on some of the time, but not all of the time. I wa

Answer 1

This should do it:

d[, distance := 1:.N - 1, by = cumsum(light)]

or this:

d[, distance := .I - .I[1], by = cumsum(light)]

And if you want to actually count number of days as opposed to row-distance, you could use:

d[, distance := as.numeric(as.POSIXct(date, format = "%m/%d/%Y") -
                           as.POSIXct(date[1], format = "%m/%d/%Y"),
                           units = 'days'),
    by = cumsum(light)]