Generating a value by substracting the value of 2 records

[RudyJamet]

In one of the fields of my attribute table, I have been trying to fill the rows with the numerical difference between the value of 2 records from another field.

Basically, in a spreadsheet, the process would be B2 = A2 - A1, B3 = A3 - A2, B4 = A4 - A3, etc.

In my attribute table, the process would look like this : the value of OID 2 in field B equals the difference between the values of OID 2 & 1 in field A.

I don't know what the script, either in Arcade or Python, could be. Does anyone have an idea?

[JohannesLindner · Accepted solution]

Python:

#YourField = 
calc(!OBJECTID!)

#Code Block
last_val = None
def calc(val):
    global last_val
    diff = (val - last_val) if last_val is not None else None
    last_val = val
    return diff

Arcade

var oid = $feature.OBJECTID
var last_row = First(OrderBy(Filter($featureset, "OBJECTID < @oid"), "OBJECTID DESC"))
if(last_row == null) { return null }
return $feature.OBJECTID - last_row.OBJECTID

[RudyJamet]

Thanks Johannes. I used the Python script and it worked fine.