Assigning a vector to a field in feature class (UpdateCursor)

Question

I don't know if my mistake is of a general nature. I come from R where it is very easy to store a vector in a matrix column. So now I (new to coding with arcpy) am desperately trying to do the same thing in ArcGIS.

I have a point feature class to which I have added a new field ("new_ID"). I want this new field to be filled with a sequence of numbers from 1 to [number of items in my FeatureClass].

Question: Is it possible to assign a vector to the new field?

The source of my problem is: I need to move and sometimes delete points in a feature class. After deleting them the column OBJECTID obviously doesn't contain a straight sequence anymore. For example: my points feature class contains 10 points, I delete point number 5, so my column OBJECTID goes like: 1,2,3,4 , 6,7,8,9,10 (5 is missing). For specific reasons I need a straight sequence of numbers. In that case after the deletion of point number 5: from 1 to 9.

I couldn't find any help in the search section. So I wonder if this problem ever occured to someone else? Am I just still to much in R? Would you solve this issue in ArcGIS completely differently? Or am I just overlooking something crucial?

I'm also unsure about which tool to use. UpdateCursor? CalculateField? JoinField?

Here's what I tried:

>>> sum = arcpy.GetCount_management("my_featureClass")
sum = int(sum.getOutput(0))
input_field = range(1, sum + 1)

>>> cursor = arcpy.UpdateCursor("my_featureClass")
for i in curs:
    i.new_ID = input_field
    curs.updateRow(i)

ValueError: Row: Invalid input value for setting

>>> cursor = arcpy.UpdateCursor("my_featureClass")
for i in curs:
    i.new_ID = input_field[i]
    curs.updateRow(i)

TypeError: list indices must be integers, not Row

>>> cursor = arcpy.UpdateCursor("my_featureClass")
for i in curs:
    i.new_ID = int(input_field)
    curs.updateRow(i)

TypeError: int() argument must be a string or a number, not 'list'

I understand why all three don't work but I don't see a solution.

Answer 1

You need to give it some indication as to which value from the input list (vector) you want for each row, which will require enumerating the cursor so you have access to an index value. Try:

sum = arcpy.GetCount_management(fc)
sum = int(sum.getOutput(0))
input = range(1, sum + 1)

cursor = arcpy.da.UpdateCursor("my_featureClass", "new_ID")
for n, row in enumerate(cursor):
    row[0] = input[n]
    cursor.updateRow(row)

This linefor n, row in enumerate(cursor) generates an index value n within that loop, which you can use to pull values out of a related list.

---

An alternative which would let you skip the sum and input variables entirely (since it's "counting" the rows as it goes through the loop):

cursor = arcpy.da.UpdateCursor("my_featureClass", "new_ID")
for n, row in enumerate(cursor):
    row[0] = n + 1
    cursor.updateRow(row)

---

I also recommend (and coded above) using the da cursors if you've got 10.1+ -- they are faster (since you can worry about only one field at a time).

Answer 2

An alternative to Erica's answer:

cursor = arcpy.da.UpdateCursor("my_featurClass", "new_ID")
i = 1
for row in cursor:
  row[0] = i
  cursor.UpdateCursor(row)
  i += 1
del cursor, row