I have a table with many instances of duplicate values.

My end goal is to have three columns:

  • "The Value": a file name. most are non-unique
  • "Duplicate Instance": "this is the 1st time this file name appears in the list", the 2nd, the 3rd, etc.
  • "Total count of Duplicates": "this file name appears 5 times in this list"

I have the Duplicate Instance from @FelixP's answer to Auto incrementing field based on groups within feature class?

I can create a separate frequency table with the Frequency tool then join that table to calculate in the total count of each file name, but I would love to skip a few steps and directly calculate the frequency in the Field Calculator interface.

Is it possible to directly calculate frequency in ArcGIS Desktop Field Calculator?

  • Does it have to be Field Calculator or can it be with code in python window?
    – BERA
    Sep 4, 2019 at 12:52
  • good point for clarification. I'd like to keep it set it up for use in the Field Calculator's "Pre-Logic Script Code" interface.
    – Zipper1365
    Sep 4, 2019 at 13:01
  • I doubt it is possible. You will have to iterate over / field calculate all rows twice and somehow save the results from first iteration and use in second. Using python window is it easier
    – BERA
    Sep 4, 2019 at 13:05
  • Yeah, I thought that might be the case - that any solution would need to but be unable to iterate through again. Still hopeful that someone might have some field calculator magic to share, though!
    – Zipper1365
    Sep 4, 2019 at 13:28
  • Similarly to gis.stackexchange.com/questions/193681/… you can go twice, however result goes to 1 field, you need 2 of them. So - script or 2 field calculations.
    – FelixIP
    Sep 4, 2019 at 18:56

2 Answers 2


If you don't find a solution using Field Calculator try python window with collections.Counter and two da.UpdateCursors:

import arcpy
from collections import Counter

fc = 'C:\data.gdb\my_riks' #Change
values = 'KKOD' #Change
dupinst = 'dupinst' #Change
totcount = 'totcount' #Change

cnt = Counter()

with arcpy.da.UpdateCursor(fc, [values, dupinst]) as cursor:
    for row in cursor:
        cnt[row[0]] += 1
        row[1] = cnt[row[0]]

with arcpy.da.UpdateCursor(fc, [values, totcount]) as cursor:
    for row in cursor:
        row[1] = cnt[row[0]]

enter image description here


Field Calculator only iterates once over the table so you cannot generate a frequency list and apply it with one pass. If this is a task you need to repeat I'd recommend using a python script outside Field Calculator or creating a model in ModelBuilder.

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