[GIS] Calculate field values using arcpy.da.UpdateCursor

arcpycursordictionarylistupdate

I am trying to create and update a field with a count of line features (tLayer) within a distance of point features (sLayer). I am attempting to use a combination of AddField_management, arcpy.da.SearchCursor, SelectLayerByLocation_management, arcpy.GetCount_management, and arcpy.da.UpdateCursor.

The code I have for this is currently updating all records for the Line_Count field with the count of the point features (i.e. 2) for only the last record. Though, a print statement following the GetCount line will return the line count for all of the point features (with a few unessential iterations). I believe it is only printing the last row in 'result' for the Line_Count update statement. Is there an efficient way for result (i.e. result=int(arcpy.GetCount_management("tLayer_lyr").getOutput(0))) to be saved as a list or an array that can be written to the Line_Count field? …Or would it be best to use a dictionary?

What do I need to do to appropriately update the Line_Count field for all of the records? Also, this process will be applied to a large dataset and will be extended to include 'where clauses'. Are there any suggestions as to how to make this as efficient as possible?

import arcpy
from arcpy import env
arcpy.env.OverwriteOutput = True

defaultGdbPath = 'C:\Topo_Check_Tess_V5.gdb'

sLayer='C:\Topo_Check_Tess_V5.gdb\Stations'
tLayer='C:\Topo_Check_Tess_V5.gdb\Lines'
#ppLayer='C:\Topo_Check_Tess_V5.gdb\Plants'

arcpy.AddField_management(sLayer, "Line_Count", "SHORT", "", "", "", "", "NULLABLE", "NON_REQUIRED", "")

TLineCountField = "Line_Count"


arcpy.MakeFeatureLayer_management(tLayer, "tLayer_lyr")
with arcpy.da.UpdateCursor (sLayer, TLineCountField) as LineCountList:
       for s_row in LineCountList:
            with arcpy.da.SearchCursor(sLayer,["OBJECTID", "SHAPE@"]) as s_list:
                    for station in s_list:
                        arcpy.SelectLayerByLocation_management("tLayer_lyr", 'WITHIN_A_DISTANCE', station[1],.000002, "NEW_SELECTION")
                        result=int(arcpy.GetCount_management("tLayer_lyr").getOutput(0))
                        print result
                        LineCountList.updateRow(s_row)
                    del station 
            del s_row

print "Done"

Updated Line_Count Field
Print readout

Best Answer

It is generally not an efficient approach (as several have commented) to use cursor processing in this way, but if you accept the performance hit (maybe you're not working with large feature classes), then you should at least eliminate the nested cursor. The update cursor can also be used as your 'read' cursor, so something like the following rewrite of your outer with block should work - this is untested:

with arcpy.da.UpdateCursor (sLayer, [TLineCountField, "SHAPE@"]) as LineCountList:
    for s_row in LineCountList:
        arcpy.SelectLayerByLocation_management("tLayer_lyr", 'WITHIN_A_DISTANCE', s_row[1], .000002, "NEW_SELECTION")
        result=int(arcpy.GetCount_management("tLayer_lyr").getOutput(0))
        print result
        s_row[0] = result
        LineCountList.updateRow(s_row)
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