Python loop script to calculate cumulative sum based on another attribute being the same

ClintonCooper1

I am looking for a script that will calculate the cumulative sum of say population (based on a presorted table that I have created) as long as the variable of ID is the same.  So it might look like

ID	POP	CUMPOP
1	100	100
1	250	350
1	150	500
2	100	100
2	500	600
3	150	150
3	600	750
3	100	850
3	150	1000

this:

jskinner

Hi Clinton,

Try the following:

import arcpy
from arcpy import env
env.workspace = r"E:\Temp\Python\test.gdb"

table = "Sample"

list = []

#append IDs to list
with arcpy.da.SearchCursor(table, ["ID"]) as cursor:
    for row in cursor:
        list.append(row[0])

del cursor

#remove duplicates
list = set(list)

#update CUMPOP field
for id in list:
    with arcpy.da.UpdateCursor(table, ["POP", "CUMPOP"], "ID = {0}".format(id)) as cursor:
        firstTime = True
        for row in cursor:            
            if firstTime:
                row[1] = row[0]
                cursor.updateRow(row)
                newVal = row[0]
                firstTime = False
            else:
                print newVal
                row[1] = row[0] + newVal
                cursor.updateRow(row)
                newVal = row[0]

del cursor