Data subset indexing tips

[#1]

I have a bunch of concatenated test runs output that have columns:  time, position, speed, etc.

... and time goes from 0 to some number, e.g. 50, then resets to zero and starts up again.

I'd like to make a new column, setid, that indexes the sets, so the first set (time 0-50) gets a "1" in the setid column, the second set (time resets to 0...) gets a "2" in the setid column, etc.

Is there a smart/easy way to do this without resorting to .jsl scripting?  

I thought about doing "New formula column" -> Row -> Diff on the time column, and the negative times would indicate start of a new set, but then I'm back to writing a custom lag formula.

[#2 · Accepted solution]

You can use a new column, index, with a formula for the group variable. The formula will look like this, assuming that the times are sequential:

If( :time > Lag( :time ), Lag( :index ), Lag( :index ) + 1 )