Calculate field values using random integer derived from count of like features

Question

I have a feature class which contains features classified by type. What I would like to do in my new field is generate a random number sequence for those like values using a count of the like values. Perhaps the example below better illustrates my question:

Field1  Field2
X       random # between 1&4
X       random # between 1&4
X       random # between 1&4
X       random # between 1&4
Y       random # between 1&2
Y       random # between 1&2
Z       random # between 1&3
Z       random # between 1&3
Z       random # between 1&3

I'm thinking I would just use GetCount for the totals and then random.randint(1, GetCount Value) to populate the new field. What I can't seem to figure out is how to have the count reset itself each time it encounters a new value. Thanks for any help you can offer.

Answer 1

Using the collections module, this is quite straightforward:

import collections, arcpy
from random import randint

#Given a list, create a dictionary containing the count of each unique item
#sumdict(["x", "x", "x", "x", "y", "y", "z", "z", "z"]) -->
#defaultdict(<type 'int'>, {'y': 2, 'x': 4, 'z': 3})
def sumdict(listvals):
    ddict = collections.defaultdict(int)    
    for val in listvals:
       ddict[val]+=1

    return ddict

#Read values from Field1 into list and "summarize counts"
dic = sumdict(row[0] for row in arcpy.da.SearchCursor(FC, ("Field1")))

with arcpy.da.UpdateCursor(shp, ("Field1", "Field2")) as cursor:
    for row in cursor:
        #Grab the value from field1 to set as upper limit for randint()
        row[1] = randint(1, dic[row[0]])

This is untested code, but it should get you started.

Edit:

For python > 2.7, sumdict() can be replaced with collections.Counter().

Answer 2

I tried this solution and it worked for me in ArcMap:

1. Open attribute table for layer

2. Get summarize for the classification field(here field1) and in step 3 of summarize form,put the name of a table. after summarize finish,the new table will be added to arcmap tables.This table contains 3 fields,ObjectId,field1 and summarization field with name Count_Field1.

3. Join source layer with this table based on Field1,now you have Count_Field1 across you other fields in layer and you can use it in field calculation.