ArcGIS - if clause in the field editor with python

Question

I have 2 columns in my table. "dB1" and "dB2" Now I want to calculate a third columnn "dB3" depending of the entries in column "dB1" and "dB2"

if "dB1" or "dB2" have an entry of "0" I want to calculate: "dB1" + "dB2"

if neither "dB1" nor "dB2" have an entry of "0" I want to calculate: 10*log(10^(0,1*"dB1")+10*(0,1*dB2))

I struggle with the syntax and the if clause here... Can someone give me the code as I theoretically know how it should be done but can't work around the syntax in python...

Answer 1

I'm guessing you mean the CalculateField tool when you refer to 'field editor with Python,' and you are in a locale that uses comas as a decimal mark (ie 0,1*dB1 = 0.1*dB1).

You can do this with a single expression:

!dB1! + !dB2! if 0 in (!dB1!,!dB2!) else 10*math.log(10**(0.1*!dB1!)+10*(0.1*!dB2!))

This uses a shorthand form of if/else:

<condition if true> if condition> else <condition if false>

0 in (!dB1!,!dB2!) is a short way of checking if either value is 0 and the rest is your formula.

This also uses uses the default base (e) for the math.log function which is the natural logarithm. If you wanted a different base, you will need to specify it to log.

Also note that field calculator uses ! to surround field names, where the SQL expression uses " (for many formats).