根据ids的相关列表重新排序集合 [英] Reordering a collection according to a related list of ids

问题描述

我有一个具有 id 属性的对象集合（无序），以及 ids 的（有序）列表。 ID列表未排序。我想在我的集合中创建一个对象列表，根据ID列表排序。

I have a Collection (unordered) of objects with an id property, and an (ordered) List of ids. The id list is not sorted. I'd like to create a List of the objects in my Collection, ordered according to the List of ids.

我没有在Guava中看到这个方法， Apache Commons - 但这正是我要找的。一个具有良好实现的库函数。

I didn't see a method for this in Guava or Apache Commons - but that's exactly what I'm looking for. A library function with a good implementation.

推荐答案

听起来你的id列表有自己的顺序;

It sounds like your id list has its own order; you're not just using the natural order, right?

这里是Guava的解决方案：

Here's the Guava solution:

Ordering.explicit(idList)
     // constructs a "fluent Comparator" that compares elements in the
     // explicitly specified order
  .onResultOf(new Function<MyObject, Id>() {
    public Id apply(MyObject o) { return o.getId(); }
   }) // make this a Comparator<MyObject> that compares on IDs
  .sortedCopy(myObjects); // get the sorted copy of the collection

就是这样。没有什么。

That's it. Nothing to it. (Disclosure: I contribute to Guava.)

或者，如果你知道ID是唯一的，它可能只是说

Alternately, if you know IDs are unique, it might just say

Map<Id, MyObject> objectsById =
  Maps.uniqueIndex(myObjects, GET_ID_FUNCTION); // defined elsewhere
List<MyObject> sortedObjects = Lists.newArrayList();
for (Id id : sortedIds) 
  sortedObjects.add(objectsById.get(id));

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