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I need to calculate a sequential ID for unique values in a field. So, for the values in Field1, the sequential ID count should count all occurrences of that value, then restart the count for the next value. For the example below, column 1 contains the values to count, column 2 is what the sequential field result should look like.

A 1

A 2

B 1

B 2

B 3

B 4

C 1

D 1

D 2

D 3

My plan was to approach this with an update cursor and the classic autoIncrement code, but it calculated all rows in the table with a sequential ID. I know the if/else is the wrong approach, but I was hoping the autoIncrement would start over within each if statement. I'm guessing I need to get a count of the unique values in Field1, then somehow calculate the sequential ID on the row as it counts? I saw a collections.Counter example, but wasn't sure if that could be applied here.

table = table path
fields = ('FIELD1,FIELD2')

rec=0
def autoIncrement():
    global rec
    pStart = 1
    pInterval = 1 
    if (rec == 0): 
        rec = pStart 
    else: 
        rec = rec + pInterval 
        return rec

with arcpy.da.UpdateCursor(table, fields) as uc:
    for row in uc:
        if row[0] == 'A':
            row[1] = str(autoIncrement())
        etc.
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2
  • Can be done using field calculator. Have a look at gis.stackexchange.com/questions/156140/… All you need is replace return 2 line with return len (...)
    – FelixIP
    Commented Aug 17, 2015 at 23:52
  • The indentation for your autoIncrement, as presented in the question, is incorrect. Please make sure that any code snippets presented work up to where you are stuck.
    – PolyGeo ♦
    Commented Aug 18, 2015 at 0:05

2 Answers 2

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2

This worked for me:

import arcpy

id_field = 'ID_Field'
calc_field = 'Calc_Field'
fc = r'C:\TEMP\points.shp'

values = []
with arcpy.da.UpdateCursor(fc, [id_field, calc_field]) as rows:
    for row in rows:
        values.append(row[0])
        row[1] = '{}{}'.format(row[0], values.count(row[0]))
        rows.updateRow(row)

print 'done'
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1
  • When I tried this the following error occurred: "...The value type is incompatible with the field type. [Calc_Field]". Based on that msg I tried it with Calc_Field as a string type field. No errors resulted, but the string output was a concatenation of ID_Field and the incremental number. So it would work IF the output was numeric and the ID_Field was dropped. I don't know Python that well, so I don't know how to fix it. Do you have any thoughts?
    – Stu Smith
    Commented Dec 23, 2017 at 1:29
0

If you want that classic auto-increment function to use.For me it is working fine-just change the variables.

import arcpy


#Set all needed variables
fc = r'C:\Users\USER_NAME\Documents\ArcGIS\Default.gdb\knp_office'
flds = ['Type','flg']
inc_fld = 'flg' # field where consecutive numbers are placed--field type is text
category_fld = 'Type' # field based on which serial/autoincrement is calculated--field type is text
vals = []


rec=0
def autoIncrement():
    global rec
    pStart = 1
    pInterval = 1 
    if (rec == 0): 
        rec = pStart 
    else: 
        rec+= pInterval 
    return rec



curU = arcpy.da.SearchCursor(fc,flds)
for row in curU:
    vals.append(row[0])
del curU
vals=set(vals)



for i in vals:
    curU=arcpy.da.UpdateCursor(fc,flds,category_fld+" = '%s'"%i)
    for row in curU:
        print "rec: "+str(rec)
        row[1] = i+" "+str(autoIncrement())
        curU.updateRow(row)
    del curU
    rec=0
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1
  • This code will not be very efficient if there are a lot of unique values as you are creating a new cursor for each one.
    – crmackey
    Commented Aug 18, 2015 at 12:22

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