Sequential ID by Two Fields

Question

Greetings.  I am working on a project trying to get sequential Plan ID numbers for polygons produced in different year and different counties.  I am using the field "County" to derive my County ID number (it is a string) and a "Year" field to derive my year value (alos a string.  The format I am looking for is:
2012-401-1
2012-401-2
2012-401-3
2012-363-1
2012-363-2
2011-401-1
2011-401-2

Any help that y'all could provide would be greatly appreciated.

S3-AllenSmithGISS · Answer

Thanks so much for your help.  Chris's code worked well in that it populated the field with the proper number.  The problem I am having is that newly digitized polygons are also numbered as 1.  Should the code be ran on the entire dataset each time after a new polygon is created?  I was hoping to assign this sequential number after the polygon is digitized when I am using sys.argvs to assign other attributes.  I can always create another tool button that runs this script on the full dataset.  Thoughts?  Thanks again.

RichardFairhurst · Answer

How about something like this: 
***untested code***import arcpy
myFC = r"C:	emp	est.shp"
yearField = "YEAR"
countyField = "COUNTY_CD"
sequenceField = "SEQUENCE" #Integer
concatField = "CONCAT" #text of sufficient length
trackingDict = {}
updateRows = arcpy.UpdateCursor(myFC)
for updateRow in updateRows:
    yearValue = updateRow.getValue(yearField)
    countyValue = updateRow.getValue(countyField)
    if (yearValue, countyValue) in trackingDict:
        trackingDict[(yearValue, countyValue)] = trackingDict[(yearValue, countyValue)] + 1
    else:
        trackingDict[(yearValue, countyValue)] = 1
    sequenceId = trackingDict[(yearValue, countyValue)]
    updateRow.setValue(sequenceField, sequenceId)
    updateRow.setValue(concatField, str(yearValue) + "-" + str(countyValue) + "-" + str(sequenceId))
updateRows.updateRow(updateRow)
del updateRow, updateRows

This code will definitely be faster, provided that the assignment of the sequential ID has no relationship to the order of any other field that is not included in the concatenated name.  That never applies for my needs (the sequential number always represents the order of one or more fields that are not included in the concatenation, such as dates, street names, or street names and measure), but if it did this would be faster.

ChrisSnyder · Answer

How about something like this: 
***untested code***import arcpy
myFC = r"C:	emp	est.shp"
yearField = "YEAR"
countyField = "COUNTY_CD"
sequenceField = "SEQUENCE" #Integer
concatField = "CONCAT" #text of sufficient length
trackingDict = {}
updateRows = arcpy.UpdateCursor(myFC)
for updateRow in updateRows:
    yearValue = updateRow.getValue(yearField)
    countyValue = updateRow.getValue(countyField)
    if (yearValue, countyValue) in trackingDict:
        trackingDict[(yearValue, countyValue)] = trackingDict[(yearValue, countyValue)] + 1
    else:
        trackingDict[(yearValue, countyValue)] = 1
    sequenceId = trackingDict[(yearValue, countyValue)]
    updateRow.setValue(sequenceField, sequenceId)
    updateRow.setValue(concatField, str(yearValue) + "-" + str(countyValue) + "-" + str(sequenceId))
updateRows.updateRow(updateRow)
del updateRow, updateRows