ArcPy Field Calculator – How to Calculate Multiple Fields Using ArcPy

arcpyfield-calculatorreclassify

I am working on adding multiple new fields to a feature and then reclassify the values based on existing fields. Here is a part of the code where it does the reclassification and I am curious if there is a cleaner way to do this considering I have around 15 fields that I want to calculate which means I would have to write 15 codeblocks, expression and a line for CalculateField_management(my assumption). The below code just shows calculation field for 2 fields. I'm rather new to the backside of Python programming, so my current code is slightly cumbersome:

import arcpy
import os, sys

arcpy.env.workspace = r'C:\Project\2022\03\test.gdb'
shapefile = "31Dec2021"

expression_1 = "Reclass(!F_MaxIntCur!)"
expression_2 = "Reclass(!Test!)"

codeblock_1 = """
def Reclass(F_MaxIntCur):
    reclass = {
        1: 1,
        1.5: 1.5,
        2: 2,
        2.5: 10,
        3: 16,
        3.5: 56,
        4: 98,
        4.5: 624,
        5: 1152
    }
    return reclass.get(F_MaxIntCur)
    """
codeblock_2 = """
def Reclass(Test):
    reclass = {
        3: "Murder-Manslaughter",
        4: "Racism",
        5: "Robbery",
        6: "Aggravated Assault",
    }
    return reclass.get(Test)
    """

arcpy.CalculateField_management(shapefile, "CurrentViolIntScore", expression_1, "PYTHON_9.3", 
                                codeblock_1)
arcpy.CalculateField_management(shapefile, "CurrentViolDescription", expression_2, "PYTHON_9.3", 
                                codeblock_2)

Best Answer

Yes, you can significantly reduce your code because update cursor lets you order fields to be updated. So for table like that:

script:

lookups=[{1:'Apple',2:'Orange'},{1:'Dog',2:'Wolf'}]
with arcpy.da.UpdateCursor("FeatureClass",['from_A','to_A','from_B','to_b']) as cursor:
    for row in cursor:
        for i in range(len(lookups)):
            aDict = lookups[i]
            k = row[2*i]
            row[2*i+1] = aDict[k]
        cursor.updateRow(row)

will result in:

Number of fields doesn't matter and your script will work much faster.

Related Solutions

[GIS] Sorting table on multiple fields using ArcPy

You could create a new empty table and use cursors to sort your data and insert the rows into the new table (this code has not been tested):

import arcpy,os

inTable = r'c:\workspace\path\in_table.dbf'
outPath = r'c:\workspace\path'
sortedTableName = r'sorted_table.dbf'
arcpy.env.workspace = outPath
arcpy.overwriteOutput = True

#--check if output table exists, if not, create it
if not os.exists(os.path.join(outPath,sortedTableName)):
    arcpy.CreateTable_management(outPath,sortedTableName)

    #--make a list of all fields in input table
    flist = arcpy.ListFields(inTable)

    #--add fields to output table
    for f in flist:
        arcpy.AddField_management(sortedTableName,f.name,f.type,f.precision,f.scale,f.length,f.aliasName)

#--if the table does exist, delete all rows so we can start fresh
else:
    try:
        arcpy.DeleteRows_management(os.path.join(outPath,sortedTableName))
    except:
        #--no rows to delete
        pass

#--create an insert cursor that will append data to output table
irows= arcpy.InsertCursor(os.path.join(outPath,sortedTableName))

#--create a search cursor to sort and then read data from input table
rows = arcpy.SearchCursor(inTable,'#','#','#','SORT_FIELD1 A;
                            SORT_FIELD2 D;
                            SORT_FIELD3 A')
for row in rows:
    #--create a new row object in the output table
    newrow = irows.newRow()
    #--populate each field
    for f in flist:
        newrow.setValue(f.name,row.getValue(f.name))
    #--insert new row
    irows.inertRow(newrow)

del irows,rows

[GIS] Calculating multiple fields using ArcPy

You need to call CalculateField_management for each field you want to calculate. E.g.

arcpy.CalculateField_management(shapefile, "Crdrt1", "[Field1]")
arcpy.CalculateField_management(shapefile, "Crdrt_min1", "[Field2]")

If you want to use a loop, you could create a dictionary that contains the fieldnames and the expressions for each field. The syntax of the expression depends on the type of database and the expression type. See here for details.

fields = {
    "Crdrt1": "[Field1]",
    "Crdrt_min1": "[Field2]"
}

existing_fields = arcpy.Describe(shapefile).fields

for field in fields:
    if not field in existing_fields:
        arcpy.AddField_management(shapefile, field, "TEXT", 0, 0, 250)
    arcpy.CalculateField_management(shapefile, field, fields[field])

Related Question

ArcPy Scripting – How to Calculate SUM of Multiple Fields into New Field