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Tom Casavant

Subjective Ranked Sorting in Python

I was working on a project and ran into a problem where I had to rank a set of objects based on an subjective value. My initial thought was to use some sort of bracket system

Ice Cream Bracket screenshot

But that doesn't fully sort out my values (Is "Vanilla" better than "Walnut"?), the next thought was writing a function to repeatedly loop through the list and compare 2 values in a round-robin sort of way. But then I realized I was just creating a sort function and we can use the existing python sort function with a slight modification to solve this

import functools
ice_cream_flavors = ["Chocolate", "Vanilla", "Raspberry", "Walnut", "Strawberry"x]


def custom_sort(x, y):
    val = input(f"Which is better '{x}' or '{y}'?\n")
    if val == x:
        return 1
    elif val == y:
        return -1
    else:
        return custom_sort(x, y)


print(sorted(ice_cream_flavors, key=functools.cmp_to_key(custom_sort)))

Ice Cream Python output screenshot

By using the functools.cmp_to_key function we can create a custom comparator and ask the user (me) to decide which is better between 2 values.

The one caveat to the method above is that I explicitly decided that no 2 values can be equal, if I were to replace that else statement with return 0 it would work just fine, but would not necessarily have the definitive order I am looking for and allow values in the list to have the same subjective rating.

One other possible issue in this setup is that there's no way to determine how much one flavor is preferred over another, which might be a useful measurement and something I'll explore in a future post.

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