topic Re: help with python in feild calculator in Python Questions

help with python in feild calculator

matu89 — Sat, 18 Jun 2022 14:12:51 GMT

hello , i have 8 points with Z value .

each 2 points is a pair ( see the colors in the image attached).

i created a new feild calles "Delta" that in their i want the result of the difference between a pair..

for example the difference between point 2 to 1 is 4.66 meters..

is there a way to do this via while or for loop ?

thanks for the help!

Re: help with python in feild calculator

DonMorrison1 — Sat, 18 Jun 2022 15:45:17 GMT

I would use a SearchCursor to read all of the Z values into a python dict - indexed by the objectid. Then loop through the feature class with an UpdateCursor calculating the Delta value for each row and writing the result

Re: help with python in feild calculator

matu89 — Sun, 19 Jun 2022 04:28:51 GMT

Hey, i dont have a clue how to start writing the code...

can you please help me with that ?

thanks..!

Re: help with python in feild calculator

JohannesLindner — Mon, 20 Jun 2022 05:46:47 GMT

Open the Python window:

Copy the script below, paste it into the Python window, edit the first line, run it

fc_path_or_layer_name = "PointsWithZValues" fields = ["OBJECTID", "Z", "Delta"] z_dict = {r[0]: r[1] for r in arcpy.da.SearchCursor(fc_path_or_layer_name, fields)} with arcpy.da.UpdateCursor(fc_path_or_layer_name, fields) as cursor: for oid, z, delta in cursor: # if OBJECTID is even, the partner oid is oid - 1 # if OBJECTID is odd, the partner id is oid + 1 partner_oid = oid + (-1 if oid % 2 == 0 else 1) delta = abs(z - z_dict[partner_oid]) cursor.updateRow([oid, z, delta])

Here, I used DoubleField as Z and TextField as Delta:

!!! The script assumes that your screenshot shows exactly what your table looks like, especially that the pairs are always odd and even ObjectID. If this isn't the case, the script gets a little more complicated (but not much) !!!

Re: help with python in feild calculator

matu89 — Mon, 20 Jun 2022 06:39:41 GMT

hey ,

thanks for your response.

i tried to run the script, but it wont run..

here is the messege :

what went wrong?

thanks!

Re: help with python in feild calculator

JohannesLindner — Mon, 20 Jun 2022 07:57:59 GMT

It couldn't find OBJECTID 2.

Clear all selections and try again. If it still doesn't work, you need the slightly more complicated script.

Re: help with python in feild calculator

matu89 — Mon, 20 Jun 2022 12:13:11 GMT

this time i get the following mmessege :

Re: help with python in feild calculator

JohannesLindner — Mon, 20 Jun 2022 13:15:05 GMT

I hate that error so much... And it could have any number of reasons.

Try a different approach:

Calculate the field, switch language to Arcade, use the script below. Be sure to clear selections!

var partner_oid = $feature.OBJECTID if($feature.OBJECTID % 2 == 0) { partner_oid -= 1 } else { partner_oid += 1 } var partner = First(Filter($featureset, "OBJECTID = @partner_oid")) if(partner == null) { return null } return Abs(partner.Z - $feature.Z)

Re: help with python in feild calculator

matu89 — Mon, 20 Jun 2022 16:08:32 GMT

that worked well!

thank you so much!

but it still interesting why the python code didnt work...