topic Re: FEATURE CLASS FIELD CALCULATION BASED ON ANOTHER FIELD in Python Questions

FEATURE CLASS FIELD CALCULATION BASED ON ANOTHER FIELD

anTonialcaraz — Sat, 11 Dec 2021 17:46:45 GMT

Hi,

I'm trying to calculate one field in the attribute table of a feature class based on another field with an if/else clause (please see script).

As a test, I used the values of "10" and "20" as results and it works. Now I need to replace that with two more complex expressions using other fields within the attribute table. That is:

Instead of "10" : 0.0006*B*(Q^0.31) *(Area_km2^0.5) *(Z_MAX/1000)*MAT

and

Instead of "20" : 0.02B(Q)^-0.31 *Area_km2^0.5 *(Z_MAX/1000)

"B"; "Q"; "Area_km2"; "Z_MAX"; "MAT" being those other fields in the attribute table.

I'm not quiet sure how to include those fields as well as the Power function within the codeblock part of the script.

Any help would be greatly appreciate it.

Many thanks

    # Add "BQART_QS" field to Nodes FC

arcpy.AddField_management(nodes, "BQART_QS", "Double")

BQART_QS_expression = "calc(!MAT!)"

codeblock = """def calc(val):
    if val >= 2:
        return 10
    else:
        return 20"""

arcpy.CalculateField_management(nodes, "BQART_QS", BQART_QS_expression, "PYTHON",codeblock)
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Re: FEATURE CLASS FIELD CALCULATION BASED ON ANOTHER FIELD

JakeSkinner — Sat, 11 Dec 2021 17:46:48 GMT

Hi AnToni,

You can use the math.pow method. I believe you would have something like the following:

BQART_QS_expression = "calc(!B!, !Q!, !Area_km2!, !Z_MAX!, !MAT!)"

codeblock = """def calc(B, Q, Area_km2, Z_MAX, MAT):
    if MAT >= 2:
        return 0.0006*B*(math.pow(Q, -31)) *(math.pow(Area_km2, 0.5)) *(Z_MAX/1000)*MAT
    else:
         return 0.02*B*(math.pow(Q, -31)) *(math.pow(Area_km2, 0.5)) *(Z_MAX/1000)"""‍‍‍‍‍‍‍

Re: FEATURE CLASS FIELD CALCULATION BASED ON ANOTHER FIELD

DanPatterson_Retired — Sat, 11 Dec 2021 17:46:50 GMT

No need for a math module

>>> import math
>>> a = 2
>>> math.pow(a,2)
4.0
>>> a**2
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Re: FEATURE CLASS FIELD CALCULATION BASED ON ANOTHER FIELD

anTonialcaraz — Tue, 18 Oct 2016 07:48:52 GMT

Thanks a lot Jake. That works perfect!

Re: FEATURE CLASS FIELD CALCULATION BASED ON ANOTHER FIELD

anTonialcaraz — Tue, 18 Oct 2016 07:49:11 GMT

Thanks very much Dan