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.
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do you mean models that are only in the list once or to shorten the list to only have one of each?Padraic Cunningham– Padraic Cunningham2014-09-25 16:24:04 +00:00Commented Sep 25, 2014 at 16:24
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build a set, i suppose?Jason Hu– Jason Hu2014-09-25 16:24:38 +00:00Commented Sep 25, 2014 at 16:24
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Also: stackoverflow.com/questions/6926928/… stackoverflow.com/questions/479897/…tom10– tom102014-09-25 16:28:30 +00:00Commented Sep 25, 2014 at 16:28
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I am not sure this is a duplicate, the OP may want to find models that only appear once which the dup will not solvePadraic Cunningham– Padraic Cunningham2014-09-25 16:30:32 +00:00Commented Sep 25, 2014 at 16:30
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4 Answers
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.
4 Comments
theodox
Many people find the curlies to read - they look like dictionaries. In that context, so as an alternative
models = list(set([car.model for car in cars]))
flaschbier
you pay quite some price for getting rid of the curlies, don't you?
Ffisegydd
Yeah I think it's because first you create the full list (with duplicates) then you add it to a set (meaning you remove the duplicates) then you put it back in a list.
Tatarize
Feed your clock cycles to the god of the anti-curlie...
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.
Comments
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']
answered Sep 25, 2014 at 16:29
Padraic Cunningham
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Now it depends on what you mean by unique. If you mean Exactly the same object then this should work:
def check_all_objects_unique(objects: List[Any]) -> bool:
unique_objects = set(objects)
if len(unique_objects) == len(objects):
return True
elif len(unique_objects) < len(objects):
return False
If by unique you mean objects with the same attribute values then other answers on here will help you.
1 Comment
R Tsch
You don't answer OPs question. This just checks if all elements are unique and in a very bad way at that. simply
return len(unique_objects) == len(objects)