blocks|key|1204573|text|我建议您改用。此数据结构专门用作从键到值集合的映射。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1204574|//uses+Enumerable.ToLookup:+the+Id+is+the+key,+and+the+User+object+the+value
var+outputNeeded+=+items.ToLookup(kvp+=>+kvp.Key,+kvp+=>+kvp.Value);|code-block|syntax|javascript|1204575|当然，如果您确实需要字典(也许是为了实现可变化性)，您可以这样做：|1204576|var+outputNeeded+=+new+Dictionary<int,+Collection<User>>();

foreach(var+kvp+in+list)
{
+++Collection<User>+userBucketForId;

+++if(!outputNeeded.TryGetValue(kvp.Key,+out+userBucketForId))+
+++{
+++++++//+bucket+doesn't+exist,+create+a+new+bucket+for+the+Id,+containing+the+user
+++++++outputNeeded.Add(kvp.Key,+new+Collection<User>+{+kvp.Value+});
+++}
+++else+
+++{+++//+bucket+already+exists,+append+user+to+it.
+++++++userBucketForId.Add(kvp.Value);
+++}
}|1204577|另外，除非您打算对Collection<T>类进行子类化，否则它并不是那么有用。你确定你不只需要一个List<User>吗|offset|length|style|CODE|1204578|entityMap^0|0|0|0|0|9|D|1E|A|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]|$M|Z|N|10|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|R|$]]

I would suggest you use a <a href="http://msdn.microsoft.com/en-us/library/bb460184.aspx" rel="nofollow"><code>Lookup&lt;TKey, TElement&gt;</code></a> instead. This data-structure is specifically intended for use as a map from keys to collections of values.

<pre><code>//uses Enumerable.ToLookup: the Id is the key, and the User object the value
var outputNeeded = items.ToLookup(kvp =&gt; kvp.Key, kvp =&gt; kvp.Value);
</code></pre>

Of course, if you do need the dictionary (to allow for mutability perhaps), you can do something like:

<pre><code>var outputNeeded = new Dictionary&lt;int, Collection&lt;User&gt;&gt;();

foreach(var kvp in list)
{
 Collection&lt;User&gt; userBucketForId;

 if(!outputNeeded.TryGetValue(kvp.Key, out userBucketForId)) 
 {
 // bucket doesn't exist, create a new bucket for the Id, containing the user
 outputNeeded.Add(kvp.Key, new Collection&lt;User&gt; { kvp.Value });
 }
 else 
 { // bucket already exists, append user to it.
 userBucketForId.Add(kvp.Value);
 }
}
</code></pre>

On another note, the<code>Collection&lt;T&gt;</code>class is not all that useful unless you intend to subclass it. Are you sure you don't just need a<code>List&lt;User&gt;</code>?

blocks|key|1204580|text|foreach+(var+u+in+items)
{
++++if+(outputNeed.Contains(u.Key))+{
++++++++outputNeed[u.Key].Add(u.Value);
++++}
++++else+{
++++++++Collection<User>+a=new+Collection<User>();
++++++++a.Add(u.Value);
++++++++outputNeed.Add(u.Key,a);
++++}
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1204581|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>foreach (var u in items)
{
 if (outputNeed.Contains(u.Key)) {
 outputNeed[u.Key].Add(u.Value);
 }
 else {
 Collection&lt;User&gt; a=new Collection&lt;User&gt;();
 a.Add(u.Value);
 outputNeed.Add(u.Key,a);
 }
}
</code></pre>

blocks|key|4786645|text|给定初始变量"item“和建议的输出变量"outputNeed"，您需要执行以下操作：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4786646|注意:这不是真正的c#/vb代码，所以请根据需要修改这个伪代码(我现在没有VS+Studio+)：|4786647|foreach+(KeyValuePair<int,+User>+pair+in+items)+
{
++++//add+a+new+collection+if+this+is+the+first+time+you+encounter+the+key
++++if+(!+outputNeed.Contains(pair.Key)+
++++{
++++++++outputNeed[pair.Key]+=+new+ArrayList<User>());
++++}
++++//add+the+user+to+the+matching+collection
++++outputNeed.Add(pair.Key,+pair.User);
}|code-block|syntax|javascript|4786648|祝好运|4786649|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Given your initial variable "item", and the suggested output variable "outputNeed", this is what you need to do:

NOTE:This is not actual c#/vb code, so please change this pseudo as required (I don't have a VS Studio at hand at the moment):

<pre><code>foreach (KeyValuePair&lt;int, User&gt; pair in items) 
{
 //add a new collection if this is the first time you encounter the key
 if (! outputNeed.Contains(pair.Key) 
 {
 outputNeed[pair.Key] = new ArrayList&lt;User&gt;());
 }
 //add the user to the matching collection
 outputNeed.Add(pair.Key, pair.User);
}
</code></pre>

Good luck

blocks|key|3375997|text|下面是一个使用LINQ的ToDictionary的例子：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3375998|var+output+=+items.GroupBy(kvp+=>+kvp.Key)
++++++++++++++++++.ToDictionary(group+=>+group.Key,
++++++++++++++++++++++++++++++++group+=>+group.Select(kvp+=>+kvp.Value).ToList());|code-block|syntax|javascript|3375999|它会产生一个Dictionary<int,List<User>>。|offset|length|style|CODE|3376000|entityMap^0|0|0|6|Q|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Here's an example using LINQ's ToDictionary:

<pre><code>var output = items.GroupBy(kvp =&gt; kvp.Key)
 .ToDictionary(group =&gt; group.Key,
 group =&gt; group.Select(kvp =&gt; kvp.Value).ToList());
</code></pre>

It results in a <code>Dictionary&lt;int,List&lt;User&gt;&gt;</code>.

blocks|key|1954255|text|以下是我的解决方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1954256|var+items+=+new+List<KeyValuePair<int,+User>>
{
++++new+KeyValuePair<int,+User>(1,+new+User+{+FirstName+=+"Name1"+}),
++++new+KeyValuePair<int,+User>(1,+new+User+{+FirstName+=+"Name2"+}),
++++new+KeyValuePair<int,+User>(2,+new+User+{+FirstName+=+"Name3"+}),
++++new+KeyValuePair<int,+User>(2,+new+User+{+FirstName+=+"Name4"+})
};

var+result+=+(
++++from+item+in+items
++++group+item.Value+by+item.Key+into+grouped
++++select+grouped
).ToDictionary(g+=>+g.Key,+g+=>+g);|code-block|syntax|javascript|1954257|DotNetFiddle|offset|length|1954258|entityMap|0|LINK|mutability|MUTABLE|url|https://dotnetfiddle.net/uTDBra^0|0|0|0|C|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

Here is my solution :
<pre><code>var items = new List&lt;KeyValuePair&lt;int, User&gt;&gt;
{
 new KeyValuePair&lt;int, User&gt;(1, new User { FirstName = &quot;Name1&quot; }),
 new KeyValuePair&lt;int, User&gt;(1, new User { FirstName = &quot;Name2&quot; }),
 new KeyValuePair&lt;int, User&gt;(2, new User { FirstName = &quot;Name3&quot; }),
 new KeyValuePair&lt;int, User&gt;(2, new User { FirstName = &quot;Name4&quot; })
};

var result = (
 from item in items
 group item.Value by item.Key into grouped
 select grouped
).ToDictionary(g =&gt; g.Key, g =&gt; g);
</code></pre>
<a href="https://dotnetfiddle.net/uTDBra" rel="nofollow noreferrer">DotNetFiddle</a>

I have the following code :

<pre><code>using System.Collections.Generic;


public class Test
{
 static void Main()
 {

 var items = new List&lt;KeyValuePair&lt;int, User&gt;&gt;
 {
 new KeyValuePair&lt;int, User&gt;(1, new User {FirstName = "Name1"}),
 new KeyValuePair&lt;int, User&gt;(1, new User {FirstName = "Name2"}),
 new KeyValuePair&lt;int, User&gt;(2, new User {FirstName = "Name3"}),
 new KeyValuePair&lt;int, User&gt;(2, new User {FirstName = "Name4"})
 };

 }
}
public class User
{
 public string FirstName { get; set; }
}
</code></pre>

Above as you can see there are multiple users for same key . Now I want to group them and convert the list object to dictionary in which the Key will be the same(1,2 as shown above) but the value will be the collection.Like this:

<pre><code> var outputNeed = new Dictionary&lt;int, Collection&lt;User&gt;&gt;();
 //Output:
 //1,Collection&lt;User&gt;
 //2,Collection&lt;User&gt;
</code></pre>

i.e they are grouped now.

How can I achieve that ?

Grouping KeyValue pairs to Dictionary

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有以下代码：using System.Collections.Generic;public class Test{ static void Main() { var items = new List<KeyValuePair<int, User>> ...

问将KeyValue对分组到字典
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