如何找到项词典集？ [英] How to Find Item in Dictionary Collection?

问题描述

我已经宣布并填充以下集合

 受保护的静态字典<字符串，字符串> _tags; 
  

现在我想看看找到集合在一个特定的条目。我尝试了以下

  thisTag = _tags.FirstOrDefault（T => t.Key ==标签）; 
如果（thisTag =默认（KeyValuePair<！字符串，字符串>））
 ... 
  

和我得到的错误：

运算符'！='不能应用于类型'的System.Collections中的操作数。 Generic.KeyValuePair'和''

起初我试图比较结果空，我想，这不是与结构所支持的。

我会一直以为找到一个项目集合中是一个非常简单的任务。 ？那么如何赫克我确定，如果我要找的项目被发现。

（注：我使用词典，因为我想快速查找。我知道我可以使用包含（）来确定，如果该项目是存在的。但是，这意味着一共有两个查找，其中排序的失败具有快速查询的目的。我会愉快地使用不同的集合，如果它能迅速查找一个项目，我有一个办法，以确定它是否是成功的。）

解决方案

  thisTag = _tags.FirstOrDefault（T => t.Key ==标签）; 
  

是一个低效率，并找到钥匙在字典中的东西一点点奇怪的方式。 。找东西的关键是一本字典的基本功能

基本的解决办法是：

 如果（_tags.Containskey（标签））{字符串myvalue的= _tags [标签] ...} 
  

但是，这需要2查找。

TryGetValue（键，超时值）更加简洁高效，它只做1查找。这回答你的问题的最后一部分：

 字符串myvalue的; 
如果（_tags.TryGetValue（标签，出myvalue的））{/ *使用myvalue的* /} 
  

I have declared and populated the following collection.

protected static Dictionary<string, string> _tags;

Now I want to look locate a particular entry in the collection. I tried the following.

thisTag = _tags.FirstOrDefault(t => t.Key == tag);
if (thisTag != default(KeyValuePair<string, string>))
    ...

And I get the error:

Operator '!=' cannot be applied to operands of type 'System.Collections.Generic.KeyValuePair' and ''

Initially I attempted to compare the result to null, and I guess that's not supported with structs.

I would've thought that finding an item within a collection is a very trivial task. So how the heck to I determine if the item I'm looking for was found?

(Note: I'm using Dictionary because I want fast lookups. I know I can use Contains() to determine if the item is there. But that means a total of two lookups, which sort of defeats the purpose of having a fast lookup. I'll happily using a different collection if it can quickly lookup an item and I have a way to determine if it was successful.)

解决方案

thisTag = _tags.FirstOrDefault(t => t.Key == tag);

is an inefficient and a little bit strange way to find something by key in a dictionary. Looking things up for a Key is the basic function of a Dictionary.

The basic solution would be:

if (_tags.Containskey(tag)) { string myValue = _tags[tag]; ... }

But that requires 2 lookups.

TryGetValue(key, out value) is more concise and efficient, it only does 1 lookup. And that answers the last part of your question:

string myValue;
if (_tags.TryGetValue(tag, out myValue)) { /* use myValue */ }

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