[GIS] How to concatenate values of two fields with update cursor with ArcPy

arcpycursornull

I have a small block of code where I concatenate two date fields and use field calculator to calculate a the values of a third field. My date fields are ORIGDTDATE and ORIGDTTIME.

How can I change the block of code that is below to concatenate the fields if the value for the row in emergency_overdue is NULL?

import arcpy     

calcExpression =  "!ORIGDTDATE!+\" \"+ !ORIGDTTIME!"

arcpy.CalculateField_management(self.line_ticket_feature_class,"emergency_overdue",calcExpression,"PYTHON_9.3")

arcpy.CalculateField_management(self.poly_ticket_feature_class,"emergency_overdue",calcExpression,"PYTHON_9.3")

Best Answer

You can create an update cursor with a where clause for only rows where emergency_overdue is null. The code below is a straight concatenation of the date and time fields, you may want to use a separator like "ORIGDTDATE" + ":" + "ORIGDTTIME".

with arcpy.da.UpdateCursor(self.line_ticket_feature_class, ["ORIGDTDATE", "ORIGDTTIME", "emergency_overdue"], "emergency_overdue IS NULL") as ucur:
    for row in ucur:
        row[2] = row[0] + row[1]
        ucur.updateRow(row)

Related Solutions

arcpy – Calculate Fields with Null Values Using arcpy.da.UpdateCursor in ArcGIS for Desktop

Here's a way to replace all the nulls with zeroes:

import arcpy
with arcpy.da.UpdateCursor(r"...gdb\test.gdb\test",["A", "B", "C"]) as cursor:
    for row in cursor:
        a_value = row[0] if row[0] else 0  # Use 0 when "A" is falsy
        b_value = row[1] if row[1] else 0  # Use 0 when "B" is falsy
        row[2] = a_value + b_value
        cursor.updateRow(row)

Note: this doesn't actually update the null values in the table; it merely replaces them with zeroes during calculations. If you want to replace the nulls with zeroes permanently, you could change the penultimate line to row = [a_value, b_value, a_value + b_value].

ArcPy – How to Iterate Fields and Remove Null Values and Spaces

I think you've got it the wrong way around. Not for field in fieldList then for row in cursor, rather for row in cursor and for field in fieldList except you will need to index properly... you're only trying to adjust the first field in the fieldList with row[0].

import arcpy

fc = "{path to geodatabase and feature class}"
fieldList = arcpy.ListFields(fc)
# remove some key fields from the list
desc = arcpy.Describe(fc)

fieldList.remove(desc.shapeFieldName)
fieldList.remove(desc.OIDFieldName)

with arcpy.da.UpdateCursor(fc, [fieldList]) as cursor:
    fRange = range(len(fieldList)) # create an index 0 to the number of elements in fieldList - 1

    for row in cursor:
        SomethingUpdated = False # a flag for changes

        # step through each field in the row by its index
        for index in fRange:
            if row[index] == None:
                row[index] = ''         #set the field to empty string
                SomethingUpdated = True #flag to store row
            else:
                val = str(row[index]).replace(" ","") # remove spaces
                if len(val) == 0:
                    # value is nothing but spaces or empty
                    row[index] = ''         #set the field to empty string
                    SomethingUpdated = True #flag to store row

        if SomethingUpdated:
            cursor.updateRow(row)

print "Processing complete"

Be aware that no checking is being done for field types; trying to set '' into a numeric field will cause this script to crash hard!

Best Answer

Related Solutions

arcpy – Calculate Fields with Null Values Using arcpy.da.UpdateCursor in ArcGIS for Desktop

ArcPy – How to Iterate Fields and Remove Null Values and Spaces

Related Question