topic Re: Field Calculator Reclass Python in Python Questions

Field Calculator Reclass Python

SamNeale — Thu, 30 Aug 2012 20:07:40 GMT

I'm trying to assign a float value to field N_Value, based on the string value in field LUCode. My code runs without errors, but isn't making any changes in the attribute table.

def Reclass(N_Value, LUCode):
  if LUCode == "Pasture":
    return 0.050
  elif LUCode == "Greenspace":
    return 0.04
  elif LUCode == "Forest":
    return 0.08
  elif LUCode == "Urban":
    return 0.04
  elif LUCode == "Brush":
    return 0.060
  elif LUCode == "Grass":
    return 0.035
  elif LUCode == "Clean, straight":
    return 0.030
  elif LUCode == "Clean, straight":
    return 0.035
  elif LUCode == "Straight, weeds/stones":
    return 0.040
  else:
    print "Done."


Reclass(!N_Value!, !LUCode!)

Thank you.

Re: Field Calculator Reclass Python

MathewCoyle — Thu, 30 Aug 2012 20:19:22 GMT

I'd remove your print statement. I'm not sure what that would do in a field calculator. Also are you using the advanced tab and calculating with python option? Try loading this and see if it does it for you.

Re: Field Calculator Reclass Python

SamNeale — Sat, 11 Dec 2021 09:41:42 GMT

I'm running it with python checked, but I'm not sure which advanced tab you're referring to.

The code runs, but it's still not updating the field. Is there a specific way that a float value needs to be written?

def Reclass(N_Value, LUCode):
  if LUCode == "Pasture":
    return 0.050
  elif LUCode == "Greenspace":
    return 0.04
  elif LUCode == "Forest":
    return 0.08
  elif LUCode == "Urban":
    return 0.04
  elif LUCode == "Brush":
    return 0.060
  elif LUCode == "Grass":
    return 0.035
  elif LUCode == "Clean, straight":
    return 0.030
  elif LUCode == "Clean, winding":
    return 0.035
  elif LUCode == "Straight, weeds/stones":
    return 0.040

Reclass(!N_Value!, !LUCode!)

Thanks

Re: Field Calculator Reclass Python

MathewCoyle — Thu, 30 Aug 2012 20:40:02 GMT

In the field calculator window there is a checkbox called show codeblock, that needs to be checked and your code needs to be split between the two boxes. If the example I sent you isn't working though I'm not sure what the issue is.

Re: Field Calculator Reclass Python

curtvprice — Sat, 11 Dec 2021 09:41:44 GMT

I'm trying to assign a float value to field N_Value, based on the string value in field LUCode. My code runs without errors, but isn't making any changes in the attribute table.

I would avoid passing N_Value to the function; you're not using it.

You also may want to consider using a dictionary instead - just nicer, faster code.

The try/except will cause the function return null if there is no match to your list of lucode values.

Calculate Value

Expr:

Reclass(!LUCode!)

Code block:

def Reclass(lucode):
  dict = {
  "Pasture"     : 0.050  ,
  "Greenspace"  : 0.04   ,
  "Forest"      : 0.08   ,
  ...
   }
  try:
    return dict[lucode]
  except:
    pass

Re: Field Calculator Reclass Python

SamNeale — Thu, 30 Aug 2012 20:43:34 GMT

Oh, yeah I have that on.

Thanks for trying.

Re: Field Calculator Reclass Python

SamNeale — Thu, 30 Aug 2012 20:49:25 GMT

Thanks, it worked! I had tried using a dictionary command before, but I didn't do it right I guess.