I have a list of objects, each having an id. This list can contain duplicates. How can I get a unique list of ids?
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4 Answers
You can add the id's as keys to a dictionary and obtain back the keys of it:
d = {}
for item in items:
d[item.id] = item
print d.keys()
Now, d.values() contains the items which have the unified ids. As long as no two different items have the same id the above is lossless.
Contrasting with other solutions (at the time of writing) this also provides a good mapping between the id and the item with the specified id.
Comments
assuming that you want a list of all id's but without doubles
all_ids = [x.getId() for x in items]
no_double_ids = list(set(all_ids))
Comments
I think the canonical way is the following:
org_list = [1,2,2,4,1,5,3]
list(set(org_list))
it does re-sort the list, so if that's an issue you need another method. See also:
How do you remove duplicates from a list in whilst preserving order? http://www.peterbe.com/plog/uniqifiers-benchmark
2 Comments
Mark Richman
That just gives me a de-duped list of objects, not the ids.
Carst
ah sorry, i misread. basically i would do what windwarrior does in his answer then...
>>> class ObjectIdHolder(object):
... def __init__(self, object_id):
... self.object_id = object_id
...
>>> ids = list(range(10)) * 2
>>> a = [ObjectIdHolder(x) for x in ids]
>>> unique_ids = {obj.object_id for obj in a}
>>> print unique_ids
set([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
