topic Re: Field calculate sequential letters in Python Questions

Field calculate sequential letters

RIMNTIR — Wed, 13 Dec 2017 22:20:46 GMT

Hello,

I am trying to figure out how I can use the field calculator with python to calculate sequential letters. For example, I would like "A,B,C,D....Z, AA,AB, AC...". I did find a code that works just fine in a regular python environment but I am having a hard time incorporating it on the field calculator.

excel - How to make a continuous alphabetic list python (from a-z then from aa, ab, ac etc) - Stack Overflow

I tried using this as the code block:

"""

from string import ascii_lowercase
import itertools

def iter_all_strings():
   size = 1
   while True:
      for s in itertools.product(ascii_lowercase, repeat=size):
            yield "".join(s)
        size +=1

"""

and "iter_all_strings()" as the expression in the field calculator but it just gives me null values.

Any help would be much appreciated, thank you.

Re: Field calculate sequential letters

DanPatterson_Retired — Wed, 13 Dec 2017 22:41:32 GMT

how big is the file? aka does it cut off at ZZ? If it is short, it might just be easier to generate the list, then slice it based on a unique ID field (perhaps OBJECTID -1 )

Re: Field calculate sequential letters

Rhys-Donoghue — Thu, 11 Aug 2022 05:19:05 GMT

This is fairly straightforward. Sorry, I don't have the time to write the code for you but if you check the end of this video I did, you can see how I used Python for creating the letters: https://www.youtube.com/watch?v=QA0iFlP0V3Y - I needed A1 to AA1 to AAA1, etc. If you're really stuck and still can't work it out, let me know and I can create a working example for you.

Re: Field calculate sequential letters

RandyBurton — Sat, 11 Dec 2021 18:58:49 GMT

Using a modified number base function, try this in the code block:

i = -1

def letterString():
    global i
    i += 1
    return toStr(i,26)

def toStr(n,base):
    convertString = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    if n < base:
        return convertString[n]
    else:
        return toStr(n//base-1,base) + convertString[n%base]‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

and this for the expression

letterString()‍‍

Basically, you will need to set up a global variable in your code block and increment it each time your function is called.

Re: Field calculate sequential letters

RandyBurton — Sat, 11 Dec 2021 18:58:52 GMT

And using your code, this would go in the code block:

from string import ascii_lowercase
import itertools

def iter_all_strings():
    size = 1
    while True:
        for s in itertools.product(ascii_lowercase, repeat=size):
            yield "".join(s)
        size +=1
        
s = iter_all_strings()
‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

The expression would be:

s.next()‍‍

The generator needs to be set up in the code block.

Re: Field calculate sequential letters

JoshuaBixby — Sat, 11 Dec 2021 18:58:54 GMT

Expression: next(values)

Expression Type: PYTHON_9.3

Code Block:

from itertools import count, product
from string import ascii_lowercase

cnt = count(1)
values = ("".join(v)
          for c in cnt
          for v in product(ascii_lowercase, repeat=c))‍‍‍‍‍‍‍

Re: Field calculate sequential letters

TedKowal — Sat, 11 Dec 2021 18:58:57 GMT

from string import ascii_uppercase
import itertools

def iter_all_strings():
    size = 1
    while True:
        for s in itertools.product(ascii_uppercase, repeat=size):
            yield "".join(s)
        size +=1

for s in itertools.islice(iter_all_strings(), 54):
    print s‍‍‍‍‍‍‍‍‍‍‍‍

Just save your stopping point in line 11 (number of iterations you want 54... I believe is "BB"

Re: Field calculate sequential letters

RIMNTIR — Thu, 14 Dec 2017 16:47:09 GMT

Randy,

Thank you very much, problem solved!

Re: Field calculate sequential letters

RandyBurton — Thu, 14 Dec 2017 17:27:25 GMT

A clean, efficient solution. Thanks for sharing bixb0012‌.