topic Re: How can I calculate a "moving" conditional evaluation in Field Calculator? in Implementing ArcGIS Questions

How can I calculate a "moving" conditional evaluation in Field Calculator?

Stefande_Bruin1 — Thu, 11 Apr 2019 09:20:02 GMT

I was wondering if anyone has ever tried doing this kind of calculation in field calculator, or if it is even possible. What I am trying to do is to calculate an order field, based on repeating polyline IDs. In excel I would do something like "If ID2 = ID1, Order1 + 1, else 1. In essence, the query refers to another column and to itself, and it refers to specific rows, sometimes other than the row being calculated. Is this doable with a VB or Python script?

Best regards

Stefan

Re: How can I calculate a "moving" conditional evaluation in Field Calculator?

DanPatterson_Retired — Thu, 11 Apr 2019 13:53:29 GMT

Sort of, but for text fields.

Table Tools for Pro on the Code Sharing site.

There are a number of tools there. Some are documented in a blog I wrote

/blogs/dan_patterson/2018/02/12/table-tools-a-set-of-tools-for-working-with-tabular-data

If you are code adept, you could modify to your specific needs, the above example was used for object subclassing and sequencing

Re: How can I calculate a "moving" conditional evaluation in Field Calculator?

JoshuaBixby — Sat, 11 Dec 2021 19:56:51 GMT

The following should work in Pro, not sure about ArcMap since it uses Python 2.x.

Code Block:

from collections import defaultdict

def counter_gen():
    counter = defaultdict(int)
    v = None
    while True:
        counter[v] += 1
        v = yield counter[v] if v else None
        
g = counter_gen()
next(g)‍‍‍‍‍‍‍‍‍‍‍

and Expression:

g.send(!ID!)‍

The code above works whether the table is sorted by ID groups or not. If the table is sorted by some other column, the code just takes the first ID value x and makes it 1, the second ID value x as 2, etc.... as it finds them.