topic Re: Splitting String at ',' accounting for No Data in Python Questions

Splitting String at ',' accounting for No Data

deleted-user-qpvAI3Fo0MKR — Thu, 10 Jan 2019 18:44:58 GMT

I've got a table with a field named Maintenance Tasks. I would like to parse the values in this field into separate fields (Task1, Task2 etc.):

I can use:

None if !MaintenanceTasks! == None else !MaintenanceTasks!.split(',')[0]

and this will parse the first item correctly into Task1, it also accounts for any null values in MaintenanceTasks.

The problem I'm running into is, for example, OID 23 above, when there's just a single item in the MaintenanceTasks field (ReplaceHead).

Any help would be greatly appreciated. FWIW I'll be scripting in Python.

Re: Splitting String at ',' accounting for No Data

DanPatterson_Retired — Sat, 11 Dec 2021 19:55:08 GMT

a = ['a, b', 'c']

for i in a:    # ---- split works properly, always returning a list
    print(i.split(","))
    
['a', ' b']
['c']

for i in a:    # ---- as evidenced below
    print(i.split(",")[0])
    
a
c‍‍‍‍‍‍‍‍‍‍‍‍‍

You can always use a code block rather than the 'smokin' one-liner

def splitter(a):
    """ """
    if i is None:
        return None
    else:
        return i.split(',')[0]

# ---- expression
splitter(!YourFieldNameHere!)‍‍‍‍‍‍‍‍‍

Re: Splitting String at ',' accounting for No Data

JoshuaBixby — Thu, 10 Jan 2019 19:07:43 GMT

In terms of style, None is a singleton so the idiomatic way to work with it is var is None. For the Task1 field, I would go with:

!MaintenanceTasks!.split(',')[0] if !MaintenanceTasks! else None‍

For the Task2 field, I would try:

!MaintenanceTasks!.split(',')[1] if !MaintenanceTasks! and ',' in !MaintenanceTasks! else None‍‍‍

Re: Splitting String at ',' accounting for No Data

DanPatterson_Retired — Sat, 11 Dec 2021 19:55:11 GMT

careful...

n = None

"," in n
Traceback (most recent call last):

  File "<ipython-input-22-0746bac53200>", line 1, in <module>
    "," in n

TypeError: argument of type 'NoneType' is not iterable

# ---- BUT str, comes to the rescue

 "," in str(n)

False

# --- amend the smokin' oneliner appropriately‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: Splitting String at ',' accounting for No Data

JoeBorgione — Thu, 10 Jan 2019 19:36:59 GMT

To add to Dan's comment: are you absolutely, 100% sure that the Maintenance Tasks values are comma separated? You may want to check for that. (Not that I've ever been burned by something like that...)

I also notice that OID 17 has three elements. Since you can't control how many elements you'll be presented (None through N), you may want to weave a len() method into your approach to determine how many elements you'll be extracting and which subsequent fields you'll be populating.

Re: Splitting String at ',' accounting for No Data

deleted-user-qpvAI3Fo0MKR — Thu, 10 Jan 2019 19:48:25 GMT

Thanks Joshua Bixby‌. This gets me to Task2. However, I have Task3, Task4, Task5, Task6 and Task7.

Any thoughts?

Re: Splitting String at ',' accounting for No Data

deleted-user-qpvAI3Fo0MKR — Thu, 10 Jan 2019 19:50:35 GMT

Thanks Joe, it is a comma - these are coming in from a list of check boxes in Survey123.

And you're right - I have up to 7 tasks in this field, so I'll need to look into the len() method.

Thanks!

Re: Splitting String at ',' accounting for No Data

JoshuaBixby — Sat, 11 Dec 2021 19:55:14 GMT

The first part of the logical check prevents the TypeError:

>>> n = None
>>> n and "," in n
>>> 
>>> n = 'string'
>>> n and "," in n
False
>>> 
>>> n = 'string,'
>>> n and "," in n
True
>>> 
‍‍‍‍‍‍‍‍‍‍‍

Re: Splitting String at ',' accounting for No Data

deleted-user-qpvAI3Fo0MKR — Thu, 10 Jan 2019 19:54:10 GMT

Just to add to my earlier reply - I thing the .count(",")+1 method might be a better idea, no?

Re: Splitting String at ',' accounting for No Data

JoshuaBixby — Thu, 10 Jan 2019 20:10:29 GMT

Seeing you have several fields, it really is a job better suited for ArcPy and an update cursor rather than the Field Calculator. That said, if you will only do this once and be done, then maybe a slightly clunky and manual way with the field calculator makes sense instead of learning how to script.

I believe the following will work, just increment the numbers starting with 0 for each new field:

!MaintenanceTasks!.split(',')[0] if !MaintenanceTasks! and !MaintenanceTasks!.count(',') >= 0 else None‍

For example, Task1 will use 0, Task2 will use 1, Task3 will use 2, etc....

Re: Splitting String at ',' accounting for No Data

JoeBorgione — Sat, 11 Dec 2021 19:55:16 GMT

I'm a list guy; gimme a list in python and I'll clean the plastic out of the oceans and get the furloughed fed works a pay check... All seriousness aside:

for i in range(len(someList)):
  do you thing...‍‍‍‍‍‍

Personal preference is all....

I like Joshua's suggestion of the using a da.UpdateCursor too....

Re: Splitting String at ',' accounting for No Data

JoshuaBixby — Thu, 10 Jan 2019 21:17:53 GMT

Joe, have you seen Ned Batchelder: Loop Like A Native ? I think you will find it worth the watch. Ned does a good job of showing how certain common patterns in other languages, e.g., for i in range(len(someList)), can be rewritten to be much more Pythonic.

Re: Splitting String at ',' accounting for No Data

JoeBorgione — Thu, 10 Jan 2019 21:22:34 GMT

I'll check it out.... thanx

Re: Splitting String at ',' accounting for No Data

deleted-user-qpvAI3Fo0MKR — Thu, 10 Jan 2019 21:49:00 GMT

Thanks Joshua Bixby‌. This will happen monthly, so I'll likely use the DA module / update cursor.

Cheers.

Re: Splitting String at ',' accounting for No Data

DanPatterson_Retired — Thu, 10 Jan 2019 22:11:03 GMT

enumerate...

try not to use …. range(len(something))

python linters will nail your code every time, and when you get used to it, it gives more and more possibilities.

good reading for the weekend Joe

Re: Splitting String at ',' accounting for No Data

JoeBorgione — Thu, 10 Jan 2019 22:32:06 GMT

cool... just tried it.....

Re: Splitting String at ',' accounting for No Data

deleted-user-qpvAI3Fo0MKR — Thu, 10 Jan 2019 22:49:25 GMT

Can you elaborate on this comment a bit, please? I'm pretty familiar with ArcPy, but this sounds more fundamental...

Re: Splitting String at ',' accounting for No Data

JoshuaBixby — Thu, 10 Jan 2019 23:03:21 GMT

I had to watch it a couple times, maybe a few, to grasp all of the points he was raising. I watched it years ago, but it really did help me start to look at iterating/iterables/sequences in a different way than other languages. Python is awesome.

Re: Splitting String at ',' accounting for No Data

JoeBorgione — Thu, 10 Jan 2019 23:03:53 GMT

I won't steal any of Dan's thunder, but take a look here: 13. Enumerate — Python Tips 0.1 documentation . It's an alternative to what I suggested. The link Joshua provides is very good as well!

Re: Splitting String at ',' accounting for No Data

DanPatterson_Retired — Sat, 11 Dec 2021 19:55:19 GMT

I hate it when you forget to press Add Comment...

A bit late, but better than never

Josh... a few enumerate things

a = ['a', 'c', 'b', 'd']

for i in range(len(a)):
    print(i)
    
0
1
2
3

for i, j in enumerate(a):
    print("{}, {}".format(i, j))
    
0, a
1, c
2, b
3, d

list(enumerate(a))
[(0, 'a'), (1, 'c'), (2, 'b'), (3, 'd')]



# ---- no need to check the length of something, enumerate is smart


a = []

list(enumerate(a))
[]


# ---- and they return the same thing, but 'enumerate' sounds cooler


for i in range(len(a)):
    print(i)
    

for i in enumerate(a):
    print(i)


# ---- ps... they both returned nothing, but an empty list
    ‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍