unique values

As part of a larger set of scripts, I needed to check for unique values in a feature class field. There are a number of manual ways to do this in ArcGIS Desktop, but here is a snippet to create a list of non-unique values and print them to the console. You could also write them to a file, or incorporate the snippet into a fix for the issue.

The basic concept is a “list within a list”. The Search Cursor is the master “list” that gets iterated over, and then values get added either to a unique value list or a duplicate value list (if they already exist in the unique value list). To speed up the analysis, I set up the Search Cursor parameters so that it only uses a single field. I don’t need any geometry or other fields in order to analyze the unique values in one field.

String formatting gets used in a couple of places here, substituting the {0} in an output string with the value in parentheses after str.format(). The “str” in the string methods represents the string you are formatting or otherwise altering. Another string method, str.join(), is used to print the list values, in this case separated by a new line: “\n”.join(list). If you wanted commas, you could use “,”.join(list).

	import arcpy

	# input feature class and field name to check for duplicates
	inputFC = r"c:\mygeodatabase.gdb\myfeatureclass"
	myField = "myField"

	# create new, empty lists for duplicate values and unique values
	dupeList = []
	uniqueList = []

	# create a search cursor with only a single field in the second parameter
	# - the one you are analyzing.
	# this is faster than the default "*" which returns all fields.
	# iterate through all the values

	with arcpy.da.SearchCursor(inputFC, [myField]) as cursor:
	for row in cursor:
	# get value in your field for this row of the ursor
	value = row[0]
	# check to see if the value already exists in the unique value list
	if value in uniqueList:
	# if it exists, append it to the list of duplicates
	dupeList.append(value)
	else:
	# if it doesn't exist, append it to the list of unique values
	uniqueList.append(value)

	# if the duplicate values list has any values, print the # of them and then list them
	if len(dupeList) > 0:
	# uses string formatting to print the number of duplicates: the "length" of the list
	# cast from an integer to a string for printing
	print("Duplicate IDs found ({0})\n".format(str(len(dupeList))))
	# prints each item in the duplicate value list separated by \n (new line)
	print("\n".join(dupeList))
	else:
	print("No duplicates found in {0} values.".format(str(len(uniqueList))))

view raw snippet-unique-values.py hosted with ❤ by GitHub

Python documentation:

ArcGIS Desktop documentation:

arcpy.da.SearchCursor

Tag: unique values

Checking for unique values in a feature class field

Unique Values