ArcPy – Iterating Over Selected Features by the Same ID

arcpycursoriteration

I have a feature class Test_NearestNeighbor_Code. This feature class has 7373 polygon features and a column/ field called osm_id. I want to do a calculation with all features that have the same osm_id. How can I do this in arcpy in an iterative way over all features (without using the ModelBuilder)?

Calculate Field code works, but loop with SearchCursor doesn't, any suggestions for improvement?

Attached the Attribute Table of the feature class Test_NearestNeigbour_Code.

with arcpy.da.SearchCursor("Test_NearestNeighbour_Code", ["osm_id"]) as cursor:
    for row in cursor:
        arcpy.management.CalculateField("Test_NearestNeighbour_Code", "Dispersitätsmaß", "nn_output[1]", "PYTHON3", 'nn_output = arcpy.stats.AverageNearestNeighbor("Test_NearestNeighbour_Code", "EUCLIDEAN_DISTANCE", "NO_REPORT", None)', "DOUBLE", "NO_ENFORCE_DOMAINS")```

Best Answer

Providing your features have unique id field called "UNIQ_ID" and osm_id is integer field the script below should work.

INPUT:

Script:

import arcpy
inLayer = "all_points"
aSet = set(row[0] for row in arcpy.da.TableToNumPyArray(inLayer,"OSM_ID"))
tempFc = "in_memory/selected"
aDict={}
for item in aSet:
    arcpy.AddMessage('Processing item %s' %item)
    arcpy.analysis.Select(inLayer, tempFc, '"osm_id" =%i'%item) #modify query if osm_id is a string
    result = arcpy.stats.AverageNearestNeighbor(tempFc)[1]
    tbl=arcpy.da.TableToNumPyArray(tempFc,"UNIQ_ID")
    for row in tbl:aDict[row[0]]=result #memorize result in dictionary
arcpy.AddMessage('Results transfer...')
with arcpy.da.UpdateCursor(inLayer,("UNIQ_ID","z_score")) as cursor:
    for oid,z in cursor:cursor.updateRow((oid,aDict[oid]))

OUTPUT:

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The SearchCursor will return geometries with the SHAPE@ token which can be used as extracting features etc.:

SHAPE@ —A geometry object for the feature.

import arcpy

feature_class = r'C:\test.gdb\polygon'

with arcpy.da.SearchCursor(feature_class,'SHAPE@') as cursor:
    for row in cursor:
        #do something with row[0]

You can of course also return field values and use for example to name the outputs. In that case use a list of tokens and fields:

with arcpy.da.SearchCursor(feature_class,['SHAPE@','field1']) as cursor:
    for row in cursor:
        #do something

row[0] will be the geometry and row[1] the value of field1

Arcpy Python Cursor – How to Search Cursor and Return Field Name If All Rows Contain a Value

The most efficient way to do it (i.e., not reading every single row in the table) is to do this...see the comments for explanation:

import arcpy
fiberCable = r'Orlando\Orlando_FIM_prep\FIBERCABLE'
field = "inventory_status_code"
# Go ahead and put the field name into the output list
output_fields = [field]
# Compose a where clause to limit the cursor to iterate over records where the field is null
where_clause = '{} IS NULL'.format(field)
with arcpy.da.SearchCursor(fiberCable, field, where_clause) as cursor:
     # If any records are null, remove the field name from the output list and then break out of the loop.
     for row in cursor:
         output_fields.remove(field)
         break

Assuming that you want to do this for multiple fields:

import arcpy
fiberCable = r'Orlando\Orlando_FIM_prep\FIBERCABLE'
fields = ["inventory_status_code", 'another_field_name']
output_fields = list()
for field in fields:
    output_fields.append(field)
    where_clause = '{} IS NULL'.format(field)
    with arcpy.da.SearchCursor(fiberCable, field, where_clause) as cursor:
         for row in cursor:
             output_fields.remove(field)
             break

By the way, never ever ever use a python keyword of any kind as a variable name (e.g., list)

Best Answer

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