ArcPy – How to Update Attributes from List of Values in Excel or CSV Table

arcpyfields-attributes

I need a Python program regarding update attributes. I have 20 shapefiles and in each shapefile, attributes to be updated based another field

My requirement is to update the codes in CODE field as per the name (Example list is given right side) for 50000 features, like if name is AAA, then code will be 419, if name is ABC, then code is 420.

I have 850 different codes and I want to update all 850 at once in shapefile. I can update two or three values by using below code but I don't know how to update 850 codes.

import arcpy
from arcpy import env


env.workspace = r"C:\\data\test.shp"   
env.workspace = fc
fclist = arcpy.ListFeatureClasses()

for fc in fclist :
   fields = ["name", "code"]

   with arcpy.da.UpdateCursor(fc, fields) as cursor:
      for row in cursor:
          if row[0] == "AAA"
              row[1] =  419
          elif:
          if .row[1] == "BBB"
              row[6] = 420
              cursor.updateRow(row)

print "codes updated"

If I want to update all 850 codes, need to write if…else statement 850 times to update all codes. I have saved all names and codes in Excel. So instead of writing many if else statements, please help how to update all codes based on name by using Excel or CSV file.

Best Answer

If you need to write a lot of if statements you should consider using a dictionary instead. Code below will read a csv file and create a dictionary of names and codes and then use the dictionary in the Updatecursor for all shapefiles in a folder. Backup your data Before you try it:

import arcpy, csv

shapefile_folder = r'C:\folder'
arcpy.env.workspace = shapefile_folder
shapefile_fields_to_update = ["name","code"]

codefile = r"C:\Program123\codes.csv"

with open(codefile, 'r') as f:
    reader = csv.reader(f)
    dict = {k:v for (k,v) in reader} #Dictionary of names and codes is created here

for shapefile in arcpy.ListFeatureClasses():
    with arcpy.da.UpdateCursor(shapefile, shapefile_fields_to_update) as cursor:
        for row in cursor:
            if row[0] in dict:
                row[1]=int(dict[row[0]]) #And used here
                cursor.updateRow(row)
            else:
                print "Name {0} not found in the dictionary, no update made for this name".format(row[0])

Related Solutions

ArcPy – Comparing Values with Next Row Using Cursor

Like @PolyGeo said, list comprehensions will help. I notice, too, that you don't define counter in your code block. Without understanding what it is, I've included it as I think you meant to have it.

    field1_list = [row[0] for row in arcpy.da.SearchCursor(tab_selektiert, ["field1"])]
    field2_list = [row[0] for row in arcpy.da.SearchCursor(tab_selektiert, ["field2"])]

    #Assuming here that counter must initialize at 1. If if should initialize at 0,
    # just change it.
    counter = 1 
    index = 0

    with arcpy.da.UpdateCursor(tab_selektiert, ["markerfield"]) as updater:
        for row in updater:
            #The value of index should never exceed len-2, since len is always
            # 1 more than the highest index value, and your function will only
            # check up to the next-to-last item in the list (the last item has
            # nothing to compare to
            if index<=len(field1_list)-2:
                n0 = field1_list[index] #The field1 value for current index
                n1 = field2_list[index] #The field2 value for the current index
                n2 = field1_list[index+1] #The field1 value for the next index
                n3 = field2_list[index+1] #The field2 value for the next index

                if n1==n2 or n3==n0 or n0==n2:
                    #EDIT: Index only increases if none of the numbers
                    # match. The markerfield is always updated with
                    # counter. 
                else:
                    #This is the condition where counter is increased
                    counter+=1

                updater.updaterRow([counter])
                index+=1

            else:
                #If you've reached the last item, update the last row with counter,
                # then break out of the loop
                updater.updateRow([counter])
                break

It's worth noting that you said counter= +1, but in python the way to do what you're trying to do is as I have it: counter+=1. I hope this helps!

ArcPy – When to Update Row Within Update Cursor with Multiple If Statements

Run your cursor.updateRow(row) just once per row that includes any changes and run it after all changes for that row. Since you change values for every row (at least for the dates), then you need to run it once for each row, after all changes for the row.

Therefore run it as the last line in the for loop, outside of any if clauses. Ie, Use only one cursor.updateRow(row) statement.

The cursor.updateRow(row) writes all values for that row at once, so there's no point running it for each value. Run it once only for the entire row.

Eg:

with arcpy.da.UpdateCursor(ci_masterpoints, flds) as cursor:
    # start looking at rows
    for row in cursor:
        row[flds.index('TodaysDate')] = datetime.datetime.now().strftime('%d/%m/%Y')
        row[flds.index('TodaysDateYr')] = datetime.datetime.now().year
        age = row[flds.index('Age')]
        # If the work order number matches to a wonum in conditions...
        if mx_row in conditions:
            row[flds.index('Leak_Location')] = conditions[mx_row]
        # Avoid null values but assign year based on Actual_Finish
        if row[flds.index('Actual_Finish')] != None:
            # Assign the year to DateInstallYr
            row[flds.index('DateInstallYr')] = row[flds.index('Actual_Finish')].year
            age = row[flds.index('TodaysDateYr')] - row[flds.index('DateInstallYr')]
        if age == None:
            row[flds.index('AgeMult')] = 1
        elif age > 10 and age < 20:
             row[flds.index('AgeMult')] = 0.9
        elif age > 20:
            row[flds.index('AgeMult')] = 0.75
        cursor.updateRow(row)

Best Answer

Related Solutions

ArcPy – Comparing Values with Next Row Using Cursor

ArcPy – When to Update Row Within Update Cursor with Multiple If Statements

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