How to get unique values from a python list of objects

Question

I have a class:

class Car:
    make
    model
    year

I have a list of Cars and want to get a list of unique models among my Cars.

The list is potentially tens of thousands of items. What's the best way to do this?

Thanks.

Answer 1

Use a set comprehension. Sets are unordered collections of unique elements, meaning that any duplicates will be removed.

cars = [...] # A list of Car objects.

models = {car.model for car in cars}

This will iterate over your list cars and add the each car.model value at most once, meaning it will be a unique collection.

Answer 2

If you want to find cars that only appear once:

from collections import Counter
car_list = ["ford","toyota","toyota","honda"]
c = Counter(car_list)
cars = [model for model in c if c[model] == 1 ]
print cars
['honda', 'ford']

Answer 3

Add a method to the class that returns a unique list

def unique(list1):
    # intilize a null list
    unique_list = []

    # traverse for all elements
    for x in list1:
        # check if exists in unique_list or not
        if x not in unique_list:
            unique_list.append(x)

    return unique_list

Otherwise,

If you're looking to pass a dictionary of make, model year then you can use pandas dataframe in order to get the unique values.