UpdateCursor with multiple loops in ArcPy

Question

I have a feature class and I need to renumber from 1 and increase by 1 for a group of features. To do that, I need to define these groups (based on atributes of a field) and for each group make an update cursor. My problem is that in my code, just the first group of features are updated and the others not. Where is my mistake?

This is what I have today

and this is what I want

My code:

import arcpy
lyrName = r"C:\Users\Moshe\Documents\ArcGIS\Default.gdb\D1"
Layer = "Layer"
RefName = "RefName"
startNumber = 1
listValue = []
with arcpy.da.SearchCursor(lyrName, Layer) as cursor:
    for row in cursor:
        value = row[0]
        listValue.append(row[0])
    list = list(dict.fromkeys(listValue))
    print(list)
Layer2 = "Layer"
RefName2 = "RefName"
with arcpy.da.UpdateCursor(lyrName, [RefName2, Layer2]) as cursor2:
    for i in list:
        print (i)
        for row2 in cursor2:
                if row2[1] in str(i):
                    row2[0] = startNumber
                    startNumber = startNumber + 1
                    cursor2.updateRow(row2)
                    print "updated row {}".format(row2[0])
        startNumber = 1

Your task is fraught with potential failures. There is no mandate that an UpdateCursor return records in a particular order if an ORDER BY is not specified. I suggest you change this multiphase update into a series of SearchCursor calls (with ORDER BY) to compile a dictionary of intended results, then use one UpdateCursor to modify values by rowid lookup. — Vince, Jun 18 '21 at 13:50
the order in my next stage. it will be determinate by the xy location. but for now. how can make this lookup? — moshe, Jun 18 '21 at 14:04
Or this https://gis.stackexchange.com/questions/200150/auto-incrementing-field-based-on-groups-within-feature-class/200154#200154 — FelixIP, Jun 22 '21 at 02:42

Jason Miller · Answer 1 · 2021-06-21T17:58:58.117

This should do what you are wanting to do...

import arcpy
lyrName = r"C:\Users\Moshe\Documents\ArcGIS\Default.gdb\D1"

fields = ["Layer", "RefName"]

counter = 1
prevFieldValue = ""
with arcpy.da.UpdateCursor(lyrName, fields, sql_clause=(None, "ORDER BY Layer, RefName")) as cursor:
    for row in cursor:
        if row[0] == prevFieldValue:
            counter += 1
        else:
            counter = 1
        row[1] = str(counter)
        cursor.updateRow(row)
        prevFieldValue = row[0]

UpdateCursor with multiple loops in ArcPy

1 Answers1