topic Re: Calculate Field with Python/ Arcade in ArcGIS Online Questions

Calculate Field with Python/ Arcade

NoahLeimgruber — Wed, 25 Nov 2020 13:00:47 GMT

HI all!

I want to execute a Python/Arcade command in ArcGIS Calculate Field which gives me a result for the catchment area (table).
The command should select all IDs in the list that have an X-value greater than the ID to be calculated (Here ID 1) and a Y-value less than the ID to be calculated (Here ID 1).
From the selected IDs, the respective areas should then be summed up and saved to the catchment area field.

In this example, the X and Y values of IDs 2 and 3 fulfill the condition. Thus, the respective areas would be added together, which would result in 15. The result would be stored in the catchment area of ID 1.

Thank you very much for your help!

ID	X	Y	area	catchment area
1	1000	2000	23	? (15)
2	1034	1083	10	…
3	1599	1743	5	…
4	1403	2004	34

Re: Calculate Field with Python/ Arcade

XanderBakker — Wed, 25 Nov 2020 18:44:04 GMT

Hi @NoahLeimgruber ,

I probably would advise you to use Python for this one and use a dictionary to store the values and easy access, although I wouldn't do this using a Field Calculation (preferably, I would use a standalone script). With Arcade you would probably end up using multiple requests on the data which would result in longer processing times.

However, is this "static" data or is this data dynamic and requires an update of this logic when data is edited? In that case I would probably go for an attribute rule using Arcade.

Just to be clear... when you calculate the catchment area for ID 1 you don't include the area of ID 1 in the result, right?

Re: Calculate Field with Python/ Arcade

NoahLeimgruber — Wed, 25 Nov 2020 19:25:12 GMT

Hello @XanderBakker

Thank you very much for your answer and your suggestions! Unfortunately I'm a **bleep** beginner when it comes to coding so I don't understand exactly what you mean in the first section.

The data is "static".

and yes that is correct, i don't want to include the area of ID 1 in the calculation

Thank you again!

Re: Calculate Field with Python/ Arcade

XanderBakker — Wed, 25 Nov 2020 23:24:09 GMT

Hi @NoahLeimgruber ,

I could write some code to do this, but it would be easier to have some (dummy) data with the same schema to test with. Any chance that you could share some (dummy) data for this?

Re: Calculate Field with Python/ Arcade

NoahLeimgruber — Thu, 26 Nov 2020 13:25:19 GMT

Hi @XanderBakker

Thank you so much, you are absolutely amazing!

I' ve created a WeTranfer link with the data inside because I could not upload the file here because it is bigger than 5MB:

https://we.tl/t-euedapBzW8

H1 refers to X and H2 to Y

by "Einzugsgeb" is meant the catchment area

Re: Calculate Field with Python/ Arcade

XanderBakker — Thu, 26 Nov 2020 13:42:25 GMT

Hi @NoahLeimgruber ,

Thanks for sharing. I will have a look and post back any results or questions that may arrise.

Re: Calculate Field with Python/ Arcade

XanderBakker — Thu, 26 Nov 2020 14:53:52 GMT

Hi @NoahLeimgruber ,

It seems to be working:

I did notice that there are some polygons that have -1 for the H1 and H2 values and many have an H2 values that is equal to H1 +1. When selecting only those polygons that are larger than H1 and smaller than H2, you will not get any resulting polygon and a catchment area of 0. Is that correct?

The code I used is:

def main(): # load arcpy import arcpy # set reference to the featureclass fc = r'D:\GeoNet\CatchmentArea\Data.shp' # change this # create dictionary with H values and areas flds1 = ("OID@", "H1", "H2", "SHAPE@AREA") dct = {r[0]: [r[1], r[2], r[3]] for r in arcpy.da.SearchCursor(fc, flds1)} # start update cursor to write the catchment areas flds2 = ("OID@", "Einzugsgeb") with arcpy.da.UpdateCursor(fc, flds2) as curs: for row in curs: # read values oidcurr = row[0] # determine catchment area catchment = SumAreaInRangeH(oidcurr, dct) row[1] = catchment curs.updateRow(row) def SumAreaInRangeH(oidcurr, dct): # function to determine catchment area sumarea = -1 if oidcurr in dct: # set reference values h1 = dct[oidcurr][0] h2 = dct[oidcurr][1] sumarea = 0 for oid, lst in dct.items(): if oid != oidcurr and lst[0] > h1 and lst[1] < h2: sumarea += lst[2] return sumarea if __name__ == '__main__': main()

Re: Calculate Field with Python/ Arcade

XanderBakker — Thu, 26 Nov 2020 15:12:47 GMT

Hi @NoahLeimgruber ,

Looking a bit closer to the results I notice that in the Northern part there are some polygons with a huge catchment area. I also notice that they are summing the same polygon areas. If this is about catchments I don't think that this is hydrologically correct, but maybe the calculation has a different purpose.

Re: Calculate Field with Python/ Arcade

NoahLeimgruber — Thu, 26 Nov 2020 17:28:35 GMT

First of all thank you for your work and your help!

I did notice that there are some polygons that have -1 for the H1 and H2 values and many have an H2 values that is equal to H1 +1. When selecting only those polygons that are larger than H1 and smaller than H2, you will not get any resulting polygon and a catchment area of 0. Is that correct?

Yes that's right, something is not 100% correct.
I just realized that it makes more sense if the H1 or H2 value can also be the same as the ID to be calculated.
So greater and equal than H1 and less and equal than H2. (not greater than H1 and less than H2)
This solves the problem with the 0 values, because at least the own area is included.

I don't understand why some attributes have a -1 value. but we lets ignore that...

Re: Calculate Field with Python/ Arcade

NoahLeimgruber — Thu, 26 Nov 2020 17:30:28 GMT

I also notice that they are summing the same polygon areas.

What do you mean by that exactly?

Re: Calculate Field with Python/ Arcade

XanderBakker — Thu, 26 Nov 2020 19:26:37 GMT

Hi @NoahLeimgruber ,

To include the min and max values in the range and also include the area of the polygon itself, you just need to change this line:

if oid != oidcurr and lst[0] > h1 and lst[1] < h2:

into this:

if lst[0] >= h1 and lst[1] <= h2:

This will assign a catchment area value to all polygons:

Re: Calculate Field with Python/ Arcade

NoahLeimgruber — Sun, 29 Nov 2020 11:18:24 GMT

hey @XanderBakker , the code works perfectly! thank you very much! you were a great help

Re: Calculate Field with Python/ Arcade

NoahLeimgruber — Mon, 18 Jan 2021 20:23:10 GMT

Hey @XanderBakker

Sorry for asking you again!

How do I need to change the code if the value to be summed up is not from the shape area ("SHAPE@AREA"), but from a field called "Q347"?

I already tried it with no luck. Maybe you have a short answer to this. If not, no worries.

Re: Calculate Field with Python/ Arcade

XanderBakker — Mon, 18 Jan 2021 20:32:20 GMT

Hi @NoahLeimgruber ,

As far as I can see you should only have to change the line...

flds1 = ("OID@", "H1", "H2", "SHAPE@AREA")

into:

flds1 = ("OID@", "H1", "H2", "Q347")

Re: Calculate Field with Python/ Arcade

NoahLeimgruber — Mon, 18 Jan 2021 20:43:20 GMT

Hi @XanderBakker

Yes, that is exactly what I tried. But then I get the following error code

ERROR 000539: Traceback (most recent call last):
File "<string>", line 39, in <module>
File "<string>", line 19, in main
File "<string>", line 34, in SumAreaInRangeH
TypeError: unsupported operand type(s) for +=: 'float' and 'NoneType'
Failed to execute (CalculateField).

Re: Calculate Field with Python/ Arcade

XanderBakker — Mon, 18 Jan 2021 20:55:10 GMT

Hi @NoahLeimgruber ,

It looks like you have None (null) values in your Q347 field.

You can put an additional validation in the function:

def SumAreaInRangeH(oidcurr, dct): # function to determine catchment area sumarea = -1 if oidcurr in dct: # set reference values h1 = dct[oidcurr][0] h2 = dct[oidcurr][1] sumarea = 0 for oid, lst in dct.items(): if oid != oidcurr and lst[0] > h1 and lst[1] < h2: if lst[2] is not None: sumarea += lst[2] return sumarea

Re: Calculate Field with Python/ Arcade

NoahLeimgruber — Mon, 18 Jan 2021 20:55:26 GMT

@XanderBakker

Okay now it just worked. the problem were " NA " values in the column " Q347 ".
Thank you very much anyway