Select priority item from list

Question

Say I have a descending ordered list in terms of preference:

person_choice = ['amy', 'bob', 'chad', 'dan', 'emily']

meaning, amy is preferred to bob , who is preferred to chad and so on.

And I have a couple more lists like these (with names appearing in no particular order and list length):

group1 = ['joyce', 'amy', 'emily', 'karen', 'rebecca']
group2 = ['chad', 'kyle', 'michael', 'neo', 'bob']
...

In each of the group1 and group2 , I would like to select the person within this list that appears in person_choice with the highest preference. So, an expected output is like this:

group1_choice = 'amy'
group2_choice = 'bob'

Assuming that for each groupX , there is at least one person appearing in person_choice , is there a one-liner to do this in Python without complicated for loop?

Answer 1

This is two-lines, but it should work:

ranks = {
    person: i
    for i, person in enumerate(reversed(person_choice))
}

max(
    group1,
    key=lambda x: ranks.get(x, -1)
)

Essentially, we put our rankings into a dictionary for fast lookup. Then, we can use Python's min to search for our priority item. In this case, I reversed the list and used max so -1 can be used as the priority for people not in the list.

Here's what it might look like in context:

group1 = ['joyce', 'amy', 'emily', 'karen', 'rebecca']
group2 = ['chad', 'kyle', 'michael', 'neo', 'bob']
person_choice = ['amy', 'bob', 'chad', 'dan', 'emily']

ranks = {
    person: i
    for i, person in enumerate(reversed(person_choice))
}


def group_choice(group, ranks):
    return max(
        group,
        key=lambda x: ranks.get(x, -1)
    )


print(group_choice(group1, ranks))
print(group_choice(group2, ranks))

Answer 2

Using max with a custom key :

person_choice = ['amy', 'bob', 'chad', 'dan', 'emily']

group1 = ['joyce', 'amy', 'emily', 'karen', 'rebecca']
group2 = ['chad', 'kyle', 'michael', 'neo', 'bob']


def choice(group):
    return max(group, key=lambda name: -person_choice.index(name) if name in person_choice else float('-inf'))


print(choice(group1))
print(choice(group2))

Result:

amy
bob