Using ArcPy UpdateCursor to Update a field

Question

In my data I have one field (L1_SOILTYP) and a new field I created (SoilClass). I am trying to use update cursor to assign classification values (1-17) based on the values found in the L1_SOILTYP field. For example... 'Clay' and 'CLAY' should be assigned '1'. I am using ArcGIS Pro for this.

Following an example on this page... https://pro.arcgis.com/en/pro-app/latest/arcpy/data-access/updatecursor-class.htm ... this is the code I have come up with...

import arcpy
fc = 'D:\GIS\PollinatorProject\Pollinator\Pollinator.gdb\soil_samples'
fields = ['L1_SOILTYP', 'SoilClass2']
with arcpy.da.UpdateCursor(fc,fields) as cursor:
 for row in cursor:
 if(row[0] == 'CLAY,DUMP'or row[0] == 'CLAY(WEATHERED SHALE)'or row[0] == 'FILL,CLAY'):
 row[1]= '1'
 elif(row[0] == 'SAND' or 'TOO SANDY' or row[0] == 'Sand, coarse' or row[0] == 'COARSE SAND'):
 row[1]= '2'
 elif(row[0] =='Sandy Clay' or row[0] == 'SAND & CLAY' or row[0] == 'SAND SOME CLAY'):
 row[1] = '3'
 
 cursor.updateRow(row)

Using this code the clay values are all correctly assigned the 1 value, but all the other soil types are assigned to 2. This is a shortened version of what I have, but each time I run the code, all values are assigned '1'

• Vince: I'd use a dictionary for this pattern. Load all the valid values in a single dictionary to start, and assign row[1] = options[row[0]] if row[0] in options else None. Then you can debug your assignment issues.
• carlymar: What I mean to say is that all the clay values are assigned to 1 and all other values are assigned to 2 ie. sand, loam, concrete when I would like them to have unique values.

Answer 1

You can use a dictionary to shorten your code:

import arcpy
fc = r'D:\GIS\PollinatorProject\Pollinator\Pollinator.gdb\soil_samples'
fields = ['L1_SOILTYP', 'SoilClass2']
type_to_class = {'CLAY,DUMP':'1', 'CLAY(WEATHERED SHALE)':'1', 'FILL,CLAY':'1',
 'SAND':'2', 'TOO SANDY':'2', 'Sand, coarse':'2', 'COARSE SAND':'2',
 'Sandy Clay':'3', 'SAND & CLAY':'3', 'SAND SOME CLAY':'3'} #Add all to dictionary
missing_types = []
with arcpy.da.UpdateCursor(fc,fields) as cursor:
 for row in cursor:
 if row[0] in type_to_class: #If you can have leading/trailing whitespaces, use if row[0].strip()
 row[1] = type_to_class[row[0]] #And here
 cursor.updateRow(row)
 else:
 missing_types.append(row[0])
 if len(missing_types)>0:
 print('Cant find soil types: {0}'.format(set(missing_types)))

Answer 2

Using BERA's suggestion this is the dictionary that was successful in creating the soil class values.

fc= r'D:\GIS\PollinatorProject\Pollinator\Pollinator.gdb\soil_samples'
fields = ['L1_SOILTYP', 'ClassofSoil']
type_to_class = {
 'CLAY, DUMP': '1',
 'DRY CLAY': '1',
 'Clay' : '1',
 'CLAY' : '1',
 'CLAY MOIST' : '1',
 'CLAY(WEATHERED SHALE)' : '1',
 'FILL, CLAY' : '1',
 'SAND' : '2',
 'TOO SANDY' : '2',
 'Sand, coarse' : '2',
 'COARSE SAND' : '2',
 'Sand' : '2',
 'CLEAN SAND' : '2',
 'VERY SANDY' : '2',
 'SANDY' : '2',
 'FINE SAND' : '2',
 'Fine Sand' : '2',
 'COURSE SAND' : '2',
 'Coures Sand' : '2',
 'Sandy Clay' :'3',
 'SAND & CLAY' :'3',
 'SAND SOME CLAY' :'3',
 'Clayey Sand' :'3',
 'CLAY SOME SAND' :'3',
 'CLAY,SOME SAND' :'3',
 'Sandy Caly' :'3',
 'SANDY CLAY' :'3',
 'COURSE SAND SOME CLAY' :'3',
 'SILT' : '4',
 'Silit' : '4',
 'SILTY' : '4',
 'Silty' : '4',
 'Silt' : '4',
 'MEDIUM' : '5',
 'FIRM' : '5',
 'NO DUMP' : '5',
 'SLAB/PLASTIC' : '5',
 'DUMP' : '5',
 'Dump' : '5',
 'TRACES OF DUMP' : '5',
 'SLAB' : '5', 
 'SOME DUMP' : '5',
 'SOME WOOD' : '5',
 'REJECTION' : '5',
 'TO 6(2)' : '5',
 'VERY SOFT' : '5',
 'WOOD' : '5',
 '2)' : '5',
 'VERY DAMP' : '5',
 'FILL' : '5',
 'SLAG': '5',
 'ASPHALT/FILL' : '6',
 'ASPHALT' : '6',
 'asphalt is newer' : '6',
 'asphalt is new' : '6',
 'Gravel & Sand' : '7',
 'SAND & GRAVEL (STRUCTURAL FILL' : '7',
 'SILTY GRAVEL & SAND' : '7',
 'GRAVLE & SAND' : '7',
 'Sand w/ Gravel' : '7',
 'COURSE SAND & GRAVEL' : '7',
 'Sand w/ gravel' : '7',
 'SAND & GRAVEL' : '7',
 'GRAVEL & SAND' : '7',
 'CLAYEY SAND & GRAVEL' : '7', 
 'Sand & Gravel' : '7',
 'SAND & gRAVEL' : '7',
 'Sand & Pea Gravel': '7', 
 'SAND & GRAVEL SOME CLAY' : '7',
 'Gravel Ballast' : '8',
 'LARGE GRAVEL' : '8',
 'GRAVEL' : '8',
 'SiltyClay' : '9',
 'Clayey Silt' :'9',
 'SILTY CALY' : '9',
 'SILTY CLAY' : '9',
 'CLAYEY SILT' : '9',
 'GRASS/TOPSOIL' :'10',
 'TOP SOIL' :'10',
 'CLAY & GRAVEL' :'11',
 'Sandy Clay & Gravel' :'11',
 'DUMP, BRICK' : '12',
 'CONCRETE' : '12',
 'RED BRICK' : '12',
 'BRICK' : '12',
 'SAND SOME BRICK' : '12',
 'Silty Sand' : '13',
 'Sandy Silt' : '13',
 'SAND & SILT' : '13',
 'SANDY SILT' : '13',
 'SILTY SAND' : '13',
 'FINE SAND SILTY' : '13',
 'BASALT & SHALE' : '14',
 'SHALE' : '14',
 'BROWN SHALE' : '14',
 'CLAY, CINDERS' : '15', 
 'CINDERS & SILT' : '15', 
 'CINDERS' : '15', 
 'SANDSTONE' : '16', 
 'CLAYEY SANDSTONE' : '16', 
 'ROCK' : '17', 
 'LOAM' : '18', 
 'n/a' : '<NULL>',
 ' ' : '<NULL>'
}
missing_types = []
with arcpy.da.UpdateCursor(fc,fields) as cursor:
 for row in cursor:
 if row [0] in type_to_class:
 row[1] = type_to_class[row[0]]
 cursor.updateRow(row)
 else: 
 missing_types.append(row[0])
 if len(missing_types)>0:
 print('Cant find soil types: {0}'.format(set(missing_types)))
 ```