The problem seems to be the line
in the If statement.
If the result dataset (initialized with test2) is smaller in length than the ori_datensatz and you try to write at an index position not present in the result dataset an error occurs.
One further problem maybe the first difference you form in the loop. For i = 0 the variable x gets the value of last value minus the first value. If the ori_dataset is assumed to be periodic, this would be exactly what you need, otherwise the first difference doesn’t make sense.
The vector features of FPScript allow you to get rid of the loop. The following expression computes a datasets of the periodic differences in one go:
Dim delta = ori_datensatz[-1] – ori_datensatz : ori_datensatz[0,-2] – ori_datensatz[1,-1]
With the aid of the FPScript functions from the Event Isolation group, you can extract the desired indices; in your case the line
dim idx = ValuesBelowLevel(delta, dtr, EVENT_INDEX+EVENT_COMPLEMENT)
will select all values strictly greater than dtr.
result[idx] = ori_datensatz[idx]
to overwrite the selected values in the dataset result.