Using Python in the field calculator - if/else over multiple fields

Question

I'm trying to work out how to populate a field depending on the lowest score across 6 other fields. I've read several other questions relating to if/else statements but I'm only just starting to learn Python so I'm struggling to put together any code that works.

I'm trying to populate a 'Main Failing' field, where for each object ID in the feature class the worst scored field out of 6 other fields will be noted.

The other fields are: 'Interconnectivity', 'PropCover', 'PatchSize', 'ShapeIndex', 'Naturalness' and 'EdgeNat' and they are all short integer, with high numbers being better than low numbers.

So for example if 'Interconnectivity' had the lowest score across the 5 fields for one objectID, I would like to work out how to populate the 'Main Failing' column for that objectID with text saying 'Interconnectivity'.

Edited: Here's an example of the code I've tried so far with Branco's help. It's running without errors but is either leaving the MainFailing field blank (if 'return resultList[0]') or is populating it with 0's (if return resultList[1]).

Codeblock:

myFunction( !InterconnectivityScore!, !PropCoverScore!, !PatchSizeScore!, !ShapeIndexScore!, !NatScore!, !EdgeNatScore!)

Pre-logic script code:

def myFunction ( interconnectivityScoreValue, propCoverScoreValue, patchSizeScoreValue, shapeIndexScoreValue, natScoreValue, edgeNatScoreValue):
resultList = ["",0]
if interconnectivityScoreValue <= resultList[1]:
    resultList[0] = "Interconnectivity"
    resultList[1] = InterconnectivityScore
if propCoverScoreValue <= resultList[1]:
    resultList[0] = "ProportionalCover"
    resultList[1] = PropCoverScore
if patchSizeScoreValue <= resultList[1]:
    resultList[0] = "PatchSize"
    resultList[1] = PatchSizeScore
if shapeIndexScoreValue <= resultList[1]:
    resultList[0] = "ShapeIndex"
    resultList[1] = ShapeIndexScore
if natScoreValue <= resultList[1]:
    resultList[0] = "Naturalness"
    resultList[1] = NatScore
if edgeNatScoreValue <= resultList[1]:
    resultList[0] = "EdgeNaturalness"
    resultList[1] = EdgeNatScore
return resultList[1]

Answer 1

Try this (edited per @alpha-beta-soup comment):

def myFunction (inter, prop, patch, shp, nat, edge):
    myList = [inter, prop, patch, shp, nat, edge]
    myList.sort()
    myDict = {'Interconnectivity' : inter,
              'PropCover' : prop,
              'PatchSize' : patch,
              'ShapeIndex': shp,
              'Naturalness' : nat,
              'EdgeNat' : edge}

    myVal = 101   # using 101 as a max + 1 possible value; adjust if needed
    myReturn = ''
    for k, v in myDict.iteritems():
        if v < myVal:
            myVal = v
            myReturn = k

    return myReturn

Note that if you have two matching low values, there's nothing to select one over the other. That would require additional checking based on whatever your criteria is. Since a dictionary is unordered, you can't control it that way.

Here's another way without dictionaries, with an optional clause for ties. You may want different logic in case of ties.

def myFunction2 (inter, prop, patch, shp, nat, edge):
    # use tuples to ensure value order
    myScoreTuple = (prop, patch, shp, nat, edge)
    myTextTuple = ('PropCover',
                   'PatchSize',
                   'ShapeIndex',
                   'Naturalness',
                   'EdgeNat')

    # initialize values
    myLowValue = inter
    myReturn = 'Interconnectivity'

    # now check for any lower value
    for i in range(len(myScoreTuple)):
        if myScoreTuple[i] < myLowValue:
            myLowValue = myScoreTuple[i]
            myReturn = myTextTuple[i]

        # optional - add multiple text values in case of tie. Remove if unneeded
        elif myScoreTuple[i] == myLowValue:
            myReturn = ', '.join((myReturn, myTextTuple[i]))

    return myReturn

Answer 2

You can do this using the field calculator and python. Make sure you have the Parser set to Python and the code block being shown.

The code I set up just uses a series of IF statements. I decided this was easier since I was comparing their scores, which I am assuming are numeric scores? In either case, I am not doing any checking for 2 scores having the same value. I am sure you can figure out that part, or figure out how to handle strings (if that is how the info is being stored). I wasn't going to worry about if, elif, etc etc... This would be run from your Main Failing field calculator. This is the main Pre-Logic Script Code: part. This outlines the function you're going to be using to process the passed in information in your *MainFailing * (Field12 for me) part. These are your function parameters.

def myFunction(interconnectivityValue, propCoverValue, patchSizeValue, shapeIndexValue, naturalnessValue, edgeNatValue):
  resultList = ["", 0]
  if interconnectivityValue <= resultList[1]:
    resultList[0] = "interconnectivity"
    resultList[1] = interconnectivityValue
  if propCoverValue <= resultList[1]:
    resultList[0] = "propCover"
    resultList[1] = propCoverValue
  if patchSizeValue <= resultList[1]:
    resultList[0] = "patchSize"
    resultList[1] = patchSizeValue 
  if shapeIndexValue <= resultList[1]:
    resultList[0] = "shapeIndex"
    resultList[1] = shapeIndexValue
  if naturalnessValue <= resultList[1]:
    resultList[0] = "naturalness"
    resultList[1] = naturalnessValue
  if edgeNatValue <= resultList[1]:
    resultList[0] = "edgeNat"
    resultList[1] = edgeNatValue
  return resultList[0]

The Main Failing part lets you specify how you want to call whatever function you declared in your Pre-Logic Script Code: section. To pass the fields for each row, notice that the field names are surrounded by !'s. This is how python knows to grab the value from the attribute table.

Using python (or VB Script) in the field calculator is a nice step towards using a more python centered approach. I would personally prefer to do this using the python interactive window and an arcpy UpdateCursor. That is another approach you can look at once you figure out the Field Calculator portion.