如何获取具有唯一属性的对象列表 [英] How to get list of objects with unique attribute

问题描述

我有一个list. 此list有许多对象.每个对象都有一个id.现在，这些对象具有不同的类型.

I have a list. This list has many objects. Each object has an id. Now the objects are of different types.

objects = [Aobject, Bobject, Cobject]

其中

>>> Aobject != Bobject
True
>>> Aobject.id ==  Bobject.id
True

问题

我想要一个基于object.id的唯一对象list.

Problem

I want a list of unique objects based on the object.id.

类似这样的东西:

set(objects, key=operator.attrgetter('id'))

(这不起作用.但是我想要这样的东西)

(This does not work. But I want something like this)

推荐答案

seen = set() 

# never use list as a variable name
[seen.add(obj.id) or obj for obj in mylist if obj.id not in seen]

之所以可行，是因为set.add返回None，因此列表推导中的表达式始终会产生obj，但前提是尚未将obj.id添加到seen中.

This works because set.add returns None, so the expression in the list comprehension always yields obj, but only if obj.id has not already been added to seen.

(如果obj is None，则表达式只能求值为None；在这种情况下，obj.id会引发异常.如果mylist包含None值，则将测试更改为if obj and (obj.id not in seen))

(The expression could only evaluate to None if obj is None; in that case, obj.id would raise an exception. In case mylist contains None values, change the test to if obj and (obj.id not in seen))

请注意，这将为您提供列表中具有给定ID的第一个对象. @Abhijit的回答将为您提供最后一个这样的对象.

Note that this will give you the first object in the list which has a given id. @Abhijit's answer will give you the last such object.

更新:

或者，ordereddict可能是一个不错的选择:

Alternatively, an ordereddict could be a good choice:

import collections
seen = collections.OrderedDict()

for obj in mylist:
    # eliminate this check if you want the last item
    if obj.id not in seen:
       seen[obj.id] = obj

list(seen.values())

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