topic Re: Task with Dictionary in Python Questions

Task with Dictionary

JohnMcoy — Fri, 05 May 2017 08:11:51 GMT

Hi,

Could you explain me, how to change field value with dictionaries?

for example :

dict = {"A" : "A-150",

"B" : "B-200",

"C" : "C-250"}

And i want change A with A-150, B with B-200

Thanks !

Re: Task with Dictionary

DanPatterson_Retired — Sat, 11 Dec 2021 23:24:16 GMT

Are you trying to retrieve the value?

dict = {"A" : "A-150",
            "B" : "B-200",
            "C" : "C-250"}

dict['A']  # get its value
'A-150'‍‍‍‍‍‍

Re: Task with Dictionary

NeilAyres — Sat, 11 Dec 2021 23:24:19 GMT

Or set it to anything.

dict["A"] = "Anything you want it to be"
‍‍‍

Re: Task with Dictionary

JohnMcoy — Fri, 05 May 2017 11:28:46 GMT

I know this, but what statement should be, if I have 2000 Fields in Values Column ? Every field in this column has A, B or C value. How to change values with dict in all 2000 fields ?

Re: Task with Dictionary

DanPatterson_Retired — Sat, 11 Dec 2021 23:24:22 GMT

def get_val(val):
    """ get a dictionary value"""
    dict = {"A" : "A-150", "B" : "B-200", "C" : "C-250"}
    return dict[val]

# python parser
# field calculator code
# field calculator expression for a text field

get_val(!YourFieldNameHere!)‍‍‍‍‍‍‍‍‍‍

Re: Task with Dictionary

JoshuaBixby — Fri, 05 May 2017 12:52:11 GMT

2000 fields? Do you mean 2000 rows? Your statement "2000 Fields in Values Column" is confusing since field and column describes the same aspect of a table.

Re: Task with Dictionary

JohnMcoy — Fri, 05 May 2017 13:00:52 GMT

Sorry, yeah I mean rows ... So like I said, I have 2000 rows and ~ 25 columns. One column is Values. So what expression would be the best ? Values column should have A-150, B-200, C-250 values. Not A,B,C. And I dont know solution for that...

Re: Task with Dictionary

DanPatterson_Retired — Fri, 05 May 2017 15:52:39 GMT

the field calculator expression I posted will work unless your table is different... post a snapshot of what you are working with so people can better understand

Re: Task with Dictionary

JohnMcoy — Mon, 08 May 2017 10:24:19 GMT

Any ideas ?

Re: Task with Dictionary

DanPatterson_Retired — Mon, 08 May 2017 12:20:27 GMT

well it is clear now that you want to do this in a script, I thought you were wanting to do this in the field calculator. That is the part that wasn't clear.

You need to use the function (ie def ) with your dictionary to make the change within your tabletocsv function but I am not sure what it is doing there. Does this work without the conversion or is it an attempt to piece a script together?

Re: Task with Dictionary

JohnMcoy — Sat, 11 Dec 2021 23:24:25 GMT

It has to be a piece of that script. You see like this part(code) if any row hasn`t a value, in CSV will write Null.

for n,i in enumerate(row):
                    if i==None:
                         row[n]="NULL"‍‍‍

So I think I need only a couple lines of code to reach a goal.

Now I have this:

for key, value in dict.items():

row[1]=value

Re: Task with Dictionary

DanPatterson_Retired — Mon, 08 May 2017 12:34:27 GMT

you still need the def example and you call it

if i is None:

row = "NULL"

else:

row = get_val(i) # get)val is the def and it needs your dictionary

Re: Task with Dictionary

BlakeTerhune — Sat, 11 Dec 2021 23:24:28 GMT

If there's no extra logic involved with getting the value, why not just look it up in the dictionary immediately instead of making a separate function?

dict = {
    "A": "A-150",
    "B": "B-200",
    "C": "C-250"
}

for n, i in enumerate(row):
    if i:
        row[n] = dict[i]
    else:
        row[n] = None‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Keep in mind that you will get a KeyError and the script will stop if i is not in the dictionary. You can use dict.get() and specify a default value if you want it to keep running.