Calculate field by comparing a field value to two other fields as min and max

Question

Using ArcMap 10.5, I'm trying to compare recommended fire regimes for different veg types (min/ max fire frequency) with actual burns from the past 10 years to see whether they are in or out of regime.... but I'm stumped on how to achieve this.

I have 2 layers:

• 'Since burnt' with attribute 'no. of years since burnt'
• 'Veg groups' with attributes 'veg type' (3 types), 'min freq' and 'max freq'

First, I spatial joined the 2 layers using 'Since burnt' as the target so now I have a table with the required fields (no of years since burnt, min freq and max freq) to do the calculation. My idea was to then add a field and populate it with 'over', 'under' or 'within' according to where the 'since burnt' value fits in the min/ max range.

With my limited knowledge of python, I came up with:

def calc(y1,y2,y3):   #where y1=yrs since burnt, y2=max, y3=min
  if y1 > y2:
    return "OVER"
  elif y1 < y3:
    return "UNDER"
  else:
    return "WITHIN"

Of course this doesn't account for equal to, which I couldn't get to work. And I assume there's a much better way of using y2, y3 as a range.

Answer 1

Since you want to compare the dates of Year-1 with the maximum Year-2 and minimum Year-3, you need to add one more condition which is:

elif y1 <= y2 and y1 >= y3:
    return "WITHIN" 

In Field calculator it will like this:

def calc(y1,y2,y3):   #where y1=yrs since burnt, y2=max, y3=min
  if y1 > y2:
    return "OVER"
  elif y1 < y3:
    return "UNDER"
  elif y1 <= y2 and y1 >= y3:
    return "WITHIN"

When executing the above function, you need to put:

calc(!Year1!,!Year2!,!Year3!) 

Applied the above function on a new field using sample data, this is the result:

Answer 2

You can check if values are in range with:

if y2 <= y1 <= y3

I think you also should check if any of the inputs are None (missing value) since for example None < 2000 will return True when this might not be what you want.

def calc(y1,y2,y3):
    if None in (y1,y2,y3):
        value = "Missing value(s)"
    elif y2 <= y1 <= y3:
        value = "WITHIN"
    elif y1 > y2:
        value = "OVER"
    else:
        value = "UNDER"
    return value

You then call the function with the acutal field names enclosed in !!, for example:

Expression:
calc(!y1!,!y2!,!y3!)