根据预排序列表对列表进行排序 [英] Sort a List based on a Pre-Sorted List

问题描述

如何基于预排序列表对列表进行排序.

How can I sort a list based on a pre-sorted list.

我有一个已排序的列表.说，我的排序列表是

I have a list which is already sorted. Say, my sorted list is

{"Junior Developer", "Developer", "Senior Developer", "Project Lead"}

现在，我想按与上述列表相同的顺序对上述列表的任何子集进行排序.也就是说，如果我有输入

Now, I want to sort any subset of the above list in the same order as the above list. That is, if I have as input

{"Developer", "Junior Developer"}，我希望输出为{"Junior Developer", "Developer"}

如果输入为{"Project Lead", "Junior Developer", "Developer"}，我希望输出为

If the input is {"Project Lead", "Junior Developer", "Developer"}, I want the output as

{"Junior Developer", "Developer", "Project Lead"}. 

我怎么能达到同样的目的?

How can I achieve the same?

推荐答案

最简单的方法是使用LINQ的.OrderBy扩展方法以及预排序集合的IndexOf方法(或等效方法).这里的想法是使用一个不同的值作为排序键"进行排序(这很有用，因为我们经常希望根据对象的属性之一对对象进行排序).

The simplest way would be to use LINQ's .OrderBy extension method, along with the IndexOf method (or equivalent) of your pre-sorted collection. The idea here is to sort using a different value as the "sort key" (this is quite useful, since often we'll want to sort objects based on one of their properties).

var sorted = listToSort.OrderBy(s => listPreSorted.IndexOf(s)).ToList();

这是一个数组示例: http://ideone.com/7oshhZ

请注意，如果您的列表非常大，这可能会很慢，因为目标列表中的每个项目都必须在预先排序的集合中依次查找(O(N * M)，其中N是目标列表的长度，M是预排序列表的长度.

Note that if your lists are very large, this will likely be slow, since each item in your target list has to be sequentially looked up in your pre-sorted collection (O(N * M), where N is the length of the target list, and M is the length of the pre-sorted list).

要克服此限制，您可以生成一个将预排序列表的项目映射到其索引的查找，然后在.OrderBy中使用此查找(运行时为O(N + M)，您可以重新运行-如果需要，请使用查找):

To overcome this limitation, you could generate a lookup mapping the items of your pre-sorted list to their indices, then use this lookup in your .OrderBy (this would have a runtime of O(N + M), and you could re-use the lookup if needed):

var preSortedLookup =
        listPreSorted.Select((v, i) => new { Key = v, Value = i })
                     .ToDictionary(kvp => kvp.Key, kvp => kvp.Value);

var sorted = listToSort.OrderBy(s => preSortedLookup[s]).ToList();

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