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Field Calculate Sequential Numbers starting with specific 18 digit number

anayoung

Hello,

I am need to field calculate sequential numbers starting with 033900000100191511. So, the numbering would be 033900000100191511, 033900000100191512, 033900000100191513 etc...

Can anyone help me with a python script for this?

With much appreciation,

Ana

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Accepted answers

DanPatterson_Retired

Ok... that is an ugly one, since you are working with strings so the simplest thing is to increment from a know easy starting point and concatenate the string to it.

try these fixes

pstart = 511

return "033900000100191" + str(rec)

can't test it, so just select a few rows and try it and report back with a screen grab of the table if possible

All comments

DanPatterson_Retired

What is the field type?

What do you have as a script so far?

anayoung

Hi,

It is a String fieldThe script I found on the field calculator help:Parser:

Python

Expression:

autoIncrement()

Code Block:

rec=0

def autoIncrement():

global rec

pStart = 1 #adjust start value, if req'd

pInterval = 1 #adjust interval value, if req'd

if (rec == 0):

rec = pStart

else:

rec = rec + pInterval

return rec

DanPatterson_Retired

Ok... that is an ugly one, since you are working with strings so the simplest thing is to increment from a know easy starting point and concatenate the string to it.

try these fixes

pstart = 511

return "033900000100191" + str(rec)

can't test it, so just select a few rows and try it and report back with a screen grab of the table if possible

anayoung

Hi Dan,

I've been trying the code but haven't been successful yet. Either it needs something different or our network problems are interfering with the calculation. I have attached a screen shot showing the field calculator with the adjusted code you provided below:

AbdullahAnter

Dan,I think this expression will calculate wrong number if the records more than 489.

because it will add a new digit and the total digits for record will be 19 digit , but Ana Young want 18 digit.

So, you should to know the count of all records that Ana have, to write the expression.

anayoung

To add to my last comment. the last three numbers just need to be unique so however that is derived it would be fine.

DanPatterson_Retired

beginning to see the pattern, but I just want to make sure that you will be starting at a known position and not from the beginning of the data set, so you will always need a start key, and then you just want to be able to extend up to ...999, then carry on using 5AA...5ZZ, 6AA...6ZZ....9AA..9ZZ which still limits your combinations but is more manageable.

anayoung

Yes, each parish in the state will have a different starting number for the sequencing. Because the first three numbers in the 18 digit number defines the parish the road is in, I won't have to worry about duplicate numbers in that regard. I'm assuming the "start key" is the "pStart" in the code?

DanPatterson_Retired

getting waylaid for a while, but some useful code in case someone else is working on this. It produces the 676 combinations of uppercase

UC = list("ABCDEFGHIJKLMNOPQRSTUVWXYZ")

cr_vals = [c + r for c in UC for r in UC]

anayoung

Hi Randy,

This would be very helpful if I knew much about generators. However, I would love to see how this code works inside of a generator. I've been looking but cannot find a simple how to set up a generator for this code. Do you know where I can find instructions? Not just broad instructions - I need step by step instructions.

anayoung

Dan and Randy...you guys are awesome! Love it!

RandyBurton

I am also new to generators, but here's my code. You might need to trap errors if you go past the limit. (Thanks to Joshua and Dan for the introduction to generators.)

def gen(x):  
    UC = list("ABCDEFGHIJKLMNOPQRSTUVWXYZ")
    cr_vals = [c + r for c in UC for r in UC]
    while True:  
        yield str(x / 676 + 5) + cr_vals[x % 676]
        x+=1

g = gen(0)

# print all combinations
for loop in range(0, 3380):
    print next(g)

JoshuaBixby

Randy, I applaud your efforts to broaden your Python knowledge and experiment with generators. Generators are one of the doors to higher-level Python functionality, so understanding and using them is worth the effort.

A couple of comments since you are learning:

Strings in Python are sequences, which means you can iterate directly over them and don't need to convert them to a list. That is, UC = "ABCD...XYZ" will work.
When working with very large sequences/sets/lists, sometimes it is advantageous to use generator expressions instead of list comprehensions since lists are fully built in memory while a generator expression is evaluated one element at a time. That is, cr_vals = (c + r for c in UC for r in UC) could also work.
A while True: loop isn't common. I used such a construct in an earlier post because I was looking for an infinite loop for my generator since I didn't want to rely on knowing the number of records ahead of time. In your case, there is a maximum number of elements (3380) so you can structure your loop differently to avoid having to use a counter and modulus operator.

def gen(start, stop, step=1):
    UC = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    for n in xrange(start, stop, step):
        for i in (str(n) + c + r for c in UC for r in UC):
            yield i

g = gen(5, 10)
for j in g:
    print j

DanPatterson_Retired

Randy... my bad on the list("AB...") thing.. I was translating a piece from a numpy snippet involved in a 'zip' which requires conversion to list in python 3.4... Joshua is right for straight python, just drop zip.

RandyBurton

Thanks Joshua for the tips and the code example. It has been most helpful in learning about generators. I hope this has also helped Ana in her project.

About the use of the modulus operator, I thought it would be easier to keep track of one number instead of two for seeding the generator for Ana's needs. If she started at 0 and did 100 records, then she would use 100 for the seed the next time. When she reaches 3380, the generator would need to be modified to produce a new sequence of codes, such as 'ZAA'.

anayoung

Way over my head, guys! But I'm enjoying the conversation. Thanks for all of the great stuff!

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