topic Is there a way to derive values using the Search Cursor and then update another field with those values? in Python Questions

Is there a way to derive values using the Search Cursor and then update another field with those values?

RPGIS — Sat, 11 Dec 2021 21:43:46 GMT

Hi,

So I have a slight predicament for this given scenario. I need to take the last 4 characters from the x coordinate and do the same for the y coordinate. I then need to combine the two and from the combined values, update another field. I have something akin but I keep running into errors. I can get it to list a set of values that I need but trying to get the update cursor to update the records in the field is tricky.

if field.name == 'FACILITY_ID':
            print field.name

            for row in arcpy.da.SearchCursor(fc, ["FACILITY_ID", "SHAPE@X", "SHAPE@Y"], """FACILITY_ID IS NULL"""):
                rowx = str(row[1])
                rowy = str(row[2])
                x = rowx[0:4]
                y = rowy[0:4]
                xy = x + y
            for row in arcpy.da.UpdateCursor(fc, ["FACILITY_ID"], """FACILITY_ID IS NULL"""):
                row.updateRow([xy])
                print '{} = {}'.format(field.name, xy)‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Any help on this would be greatly appreciated.

Re: Is there a way to derive values using the Search Cursor and then update another field with those values?

JoshuaBixby — Sat, 11 Dec 2021 21:43:48 GMT

What is going on with Line #01, are you just missing an if statement?

Try the following:

if field.name == 'FACILITY_ID':
            print field.name
            
            with arcpy.da.UpdateCursor(fc, ["FACILITY_ID", "SHAPE@X", "SHAPE@Y"], """FACILITY_ID IS NULL""") as cur:
                for fid, x, y in cur:
                    xy = str(x)[:4] + str(y)[:4]
                    cur.updateRow([xy, x, y])‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: Is there a way to derive values using the Search Cursor and then update another field with those values?

RandyBurton — Sat, 11 Dec 2021 21:43:51 GMT

You don't need both a SearchCursor and an UpdateCursror. Just use the UpdateCursor:

with arcpy.da.UpdateCursor(fc,['FACILITY_ID', 'SHAPE@X', 'SHAPE@Y'],'''FACILITY_ID IS NULL''') as cursor:
    for row in cursor:
        x = str(abs(int(row[1])))[:4]
        y = str(abs(int(row[2])))[:4]
        row[0] = x + y # concatenate strings x and y
        cursor.updateRow(row)‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

If you really want to use the x and y coordinates to create a facility ID, you may wish to format the x/y in such a way to consistently get your number. These values will be a type float, with a decimal somewhere. It may also be a negative number. So both a minus sign and a decimal may appear in your concatenation string. I converted these values to a positive integer before taking the right 4 digits. It should also be noted that the facility ID may not be unique, and it is a string so the facility ID should be type text.

Re: Is there a way to derive values using the Search Cursor and then update another field with those values?

RPGIS — Thu, 10 Oct 2019 17:40:27 GMT

Thank you very much Joshua. I thought for some reason that if I wrote the script to Search Cursor then it could only be written to search cursor. I wasn't quite sure how to combine the search and update cursors into one, or if there was a way to run one then the other. The other concern that I had (this is probably due to my limited understanding of python) is I was afraid that if I set the update cursor with the SHAPE@X and SHAPE@Y that those records in those fields might get populated. If that isn't the case then I worried for nothing.

I will give your script a try and let you know how it goes.

Also, I forgot to include the elif when I copied this script into my question. I will go back and change it so that way there is no confusion or anything.

Re: Is there a way to derive values using the Search Cursor and then update another field with those values?

RPGIS — Thu, 10 Oct 2019 17:43:24 GMT

Thanks Randy.

I tried just using the update cursor but I wasn't sure if I used the update cursor with the shape@x or shape@y if it would work. I will also try your script as well.

Robert

Re: Is there a way to derive values using the Search Cursor and then update another field with those values?

RPGIS — Thu, 10 Oct 2019 18:09:38 GMT

Hi Randy,

Your script worked and it also raised another question/concern that I have. I don't know if I should post another question or if it is fine posting it here.

When there are several fields listed for the update cursors, like what you and Joshua posted, is there a way to specify which particular field gets updated? I wasn't quite sure if there was, but part of the reason I wrote some of my scripts like what I posted, is because I wasn't sure if there was a way to do so. Your example worked and I wasn't sure if something akin to that would work. So is it possible list multiple fields and only have specific records in one of the fields get populated. Also, does this also work for a set of records in multiple fields?

Any clarity on this would help me better understand how to go about writing these kind of scripts better.

Thanks,

Robert

Re: Is there a way to derive values using the Search Cursor and then update another field with those values?

JoshuaBixby — Thu, 10 Oct 2019 18:25:13 GMT

The cursor.updateRow() method requires the list passed to it match the number of fields in the cursor. If you want to update one field out of three, just pass the original values back to the method for the 2 fields you don't want to change.

Re: Is there a way to derive values using the Search Cursor and then update another field with those values?

RandyBurton — Sat, 11 Dec 2021 21:43:54 GMT

Each row in the update cursor contain a list of the field values returned. In this case:

the field list:  ['FACILITY_ID', 'SHAPE@X', 'SHAPE@Y']

row[0] = FACILITY_ID
row[1] = SHAPE@X
row[2] = SHAPE@Y‍‍‍‍‍

So changing the value of row[0] would cause the facility ID to be updated. I suppose in reality all the fields in the row are actually updated, it is just that unless the value has been changed, the update would not be noticeable.

Instead of using indexing (ie. row[0]), you can use Joshua Bixby's approach to read the cursor into specific named variables. This might be an easier way to keep things organized. See the last three lines in Joshua's code. In line 4 of his code, change the SearchCursor to an UpdateCursor (I think this was just a typo).

Hope this helps.

Re: Is there a way to derive values using the Search Cursor and then update another field with those values?

JoshuaBixby — Thu, 10 Oct 2019 18:39:34 GMT

Thanks for the catch Randy; yes, it was a typo. I have updated the original code snippet I replied with.

UDPATE: Argh, updated again. Man, I was not paying attention writing code this morning.

Re: Is there a way to derive values using the Search Cursor and then update another field with those values?

RPGIS — Thu, 10 Oct 2019 19:14:36 GMT

Thanks Randy for clarifying. I really wasn't quite sure if setting the update cursor with multiple fields listed as the cursor would result in all of those field records being updated, much less being able to specify which of the fields in the list need updating. I also didn't know that you could specify field names in a cursor as named variables like the one Joshua posted. I will try his script again, but I will also try it with another part of the script that I am working on.

I wish there was more information like what you and Joshua provided available. I tried researching to find the best approach with the scripts that I am working on, and I wasn't able to find much.

Thanks again Randy and Joshua for the much needed help. I haven't been scripting much and I found the opportunity to when I told my supervisor that it would be easier to automate populating certain fields rather than manually doing so. My scripting knowledge is still very limited so I tend to ask around and see if anyone else can provide a better solution for what I am trying to accomplish.

If you, Joshua, or anyone else has any tips to that would help with improvements I would definitely be open to it.

Re: Is there a way to derive values using the Search Cursor and then update another field with those values?

JoshuaBixby — Thu, 10 Oct 2019 20:29:50 GMT

What I did in the code with assigning values is commonly called sequence/iterable unpacking, sometimes people call it tuple unpacking. In Python 3, it was greatly enhanced to make it more useful (PEP 3132 -- Extended Iterable Unpacking | Python.org ), but you can only use the new features with Pro.

Re: Is there a way to derive values using the Search Cursor and then update another field with those values?

RPGIS — Thu, 10 Oct 2019 23:03:56 GMT

Thanks again Joshua. I didn't even know that it was possible to unpack a

sequence by simply assigning values to the sequence. I will try applying

that to some of the other scripts since I've been looking for that kind of

solution. So regardless of how many values are in a sequence, you can

quintessentially assign values to any of the values in the sequence.

Re: Is there a way to derive values using the Search Cursor and then update another field with those values?

RPGIS — Sat, 11 Dec 2021 21:43:56 GMT

Hi Joshua,

I have another question in regards to unpacking sequences. Is it possible to specify a range of sequences and then check to see if a certain condition is true for that range. So for instance,

with arcpy.da.UpdateCursor(fc, ["fieldA", "fieldB", "fieldC", "fieldD", "COLLECTED_BY"]) as cursor:                
            for abandoned, facid, locate, survey, collected in cursor:
                if abandoned is None or abandoned == '':
                    print field.name
                    abandoned = 'NO'
                    print '{} = {}'.format(field.name, abandoned)
                    
                elif facid is None or facid == '':
                    print field.name
                    x = str(abs(int(row[1])))[:4]
                    y = str(abs(int(row[2])))[:4]
                    facid = x + y # concatenate strings x and y
                    print '{} = {}'.format(field.name, x + y)

                elif (locate, survey, collected) is None or (locate, survey, collected) == '':
                    locate = 'GPS'
                    survey = 'SUBMETER GPS'
                    collected = 'CONSULTANT'
                    print '{} = {}, {}, {}'.format(field.name, locate, survey, collected)
                    
                elif locate is None and (survey, collected) is not None:
                    locate = 'GPS'
                    print '{} = {}'.format(field.name, locate)
                    
                elif locate == 'GPS' and (survey is None or survey == '') and collected == 'CONSULTANT'
                    survey = 'SUBMETER GPS'
                    print '{} = {}'.format(field.name, locate)
                    
                elif locate == 'FIELD CHECK' and (survey is None or survey == '') and collected == 'CLIFF':
                    survey = 'ORTHO'
                    print '{} = {}'.format(field.name, survey)
                    
                elif (locate, survey) is not None and collected is None or collected == '':
                    collected = 'CONSULTANT'
                    print '{} = {}'.format(field.name, collected)
                    
                else:
                    print 'No null fields'
                cursor.updateRow(abandoned, facid, locate, survey, collected)‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

If this is by no means possible or you or Randy or anybody in general may have a better solution for this I would definitely like to hear it. I took a look at my previous script that I wrote and noticed I had the same lines of code repeating and thought that this solution( if it can be counted as one ) would be easier to utilize. Any thoughts or ideas on this would be very appreciated.

Robert

Re: Is there a way to derive values using the Search Cursor and then update another field with those values?

JoshuaBixby — Fri, 11 Oct 2019 15:12:24 GMT

So regardless of how many values are in a sequence, you can quintessentially assign values to any of the values in the sequence.

I don't quite get what you are saying/asking, especially "assign values to any of the values." Most values are singletons, so you don't assign values to values, but you do assign values to variables.

Regarding the question I think you are asking, the answer is no for Python 2 and sort of for Python 3. With Python 2, the number of variables on the left must equal the length of the sequence. With Python 3, you can utilize a wild card so the number of variables on the left don't have to equal the length of the sequence, but there are limits to what can be done with the wild card.

Re: Is there a way to derive values using the Search Cursor and then update another field with those values?

JoshuaBixby — Sat, 11 Dec 2021 21:43:59 GMT

Before getting into the question itself, there are some structural issues with your code I want to discuss first.

Many of your conditional checks in your elif statements are not working the way you think. For example, neither of the following

(locate, survey, collected) is None
(locate, survey, collected) == ''‍‍

will ever evaluate to True. Nothing within a tuple, list, or similar data structure will ever evaluate to None, not even an empty tuple.

>>> tuple() is None
False‍‍

The same holds for your empty string check.

If you are interested in checking whether all the tuple items are None, then use all() — Python 2.7.17rc1 documentation, or use any() — Python 2.7.17rc1 documentation if you are interested in checking if at least 1 is None.

>>> any(i is None for i in ('foo', 'bar', None))
True
>>> all(i is None for i in ('foo', 'bar', None))
False
>>> ‍‍‍‍‍

The use of any() and all() is complicated a little by the presence of None, since None is false-y and so are empty strings and zero.

Re: Is there a way to derive values using the Search Cursor and then update another field with those values?

RPGIS — Fri, 11 Oct 2019 19:26:18 GMT

Thanks Joshua,

I gave it some more thought this morning and took another look at the script. I was trying to figure out the best way to determine how to go about this script. Essentially I am trying to go through each of the fields and populate any null or blank values. I must have misunderstood what you meant by sequence unpacking and I think I improperly applied it.

As for my other issue, I have been trying to figure out the best way to identify blank values in a field. For some reason using none didn't seem to work and trying to use ' ' to see if it could identify those values didn't seem to work either. I will modify the script with your suggestions and see if that makes a difference. The script I posted was a modified version of another script. The other script has each field broken down so I will modify that one. I will take a look at the link one I get a chance. I am juggling several things so I have been pretty busy and that is part of the reason I am looking to automate several tasks.