C# 自定义字典获取 - 从 IEnumerable 转换回来

发布于 2024-08-27 05:47:35 字数 533 浏览 5 评论 0原文

场景

我已经在同一网站上读过一篇关于此问题的文章，但没有成功，我感觉有点困惑，但我确信我以前已经这样做过。

我有一本字典。我想从字典中获取前 200 个值。

代码

  Dictionary<int,SomeObject> oldDict = new Dictionary<int,SomeObject>();
  //oldDict gets populated somewhere else.
  Dictionary<int,SomeObject> newDict = new Dictionary<int,SomeObject>();
  newDict = oldDict.Take(200).ToDictionary();

显而易见，take 返回一个 IEnumerable，因此您必须运行 ToDictionary() 将其转换回相同类型的字典。然而，它就是不起作用，它需要一些随机键选择器的东西 - 或者什么？我什至尝试过只是铸造它，但没有成功。有什么想法吗？

原文

Scenario

Having already read a post on this on the same site, which didn't work, I'm feeling a bit stumped but I'm sure I've done this before.

I have a Dictionary.
I want to take the first 200 values from the Dictionary.

CODE

  Dictionary<int,SomeObject> oldDict = new Dictionary<int,SomeObject>();
  //oldDict gets populated somewhere else.
  Dictionary<int,SomeObject> newDict = new Dictionary<int,SomeObject>();
  newDict = oldDict.Take(200).ToDictionary();

OBVIOUSLY, the take returns an IENumerable, so you have to run ToDictionary() to convert it back to a dictionary of the same type. HOWEVER, it just doesn't work, it wants some random key selector thing - or something? I have even tried just casting it but to no avail.
Any ideas?

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中二柚 2024-09-03 05:47:35

试试这个：

newDict = oldDict.Take(200).ToDictionary(x => x.Key, x => x.Value);

基本上，字典允许您迭代键/值对；当您想要将转换回为字典时，您必须说明使用什么作为键以及使用什么作为值。

但是，我会质疑你的代码的正确性 - 因为字典没有“前 200 个值”的概念。不要依赖字典中的顺序。这基本上会为您提供字典中的一些有效的任意 200 个条目。

你想做什么？您对“前”200 个条目有何看法？

Try this:

newDict = oldDict.Take(200).ToDictionary(x => x.Key, x => x.Value);

Basically a dictionary allows you to iterate over key/value pairs; when you want to convert back to a dictionary, you have to say what to use as the key and what to use as the value.

However, I would question your code's correctness - because a dictionary doesn't have the concept of "the first 200 values". Don't rely on the ordering within a dictionary. This will basically give you some effectively-arbitrary 200 entries from within the dictionary.

What are you trying to do? What's your idea of the "first" 200 entries?

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