blocks|key|1306073|text|使用Skip，然后使用Take。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1306074|yourEnumerable.Skip(4).Take(3).Select(+x=>x+)

(from+p+in+intList.Skip(x).Take(n)+select+p).sum()|code-block|syntax|javascript|1306075|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/bb358985.aspx^0|2|4|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

Use <a href="http://msdn.microsoft.com/en-us/library/bb358985.aspx" rel="noreferrer">Skip</a> then Take.

<pre><code>yourEnumerable.Skip(4).Take(3).Select( x=&gt;x )

(from p in intList.Skip(x).Take(n) select p).sum()
</code></pre>

blocks|key|1306114|text|对于较大的列表，单独的扩展方法可能更适合于性能。我知道这对于最初的情况不是必需的，但是Linq+(to+objects)实现依赖于迭代列表，所以对于大的列表，这可能是(毫无意义的)昂贵的。实现这一点的简单扩展方法可以是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1306115|public+static+IEnumerable<TSource>+IndexRange<TSource>(
++++this+IList<TSource>+source,
++++int+fromIndex,+
++++int+toIndex)
{
++++int+currIndex+=+fromIndex;
++++while+(currIndex+<=+toIndex)
++++{
++++++++yield+return+source[currIndex];
++++++++currIndex%2B%2B;
++++}
}|code-block|syntax|javascript|1306116|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

For larger lists, a separate extension method could be more appropriate for performance. I know this isn't necessary for the initial case, but the Linq (to objects) implementation relies on iterating the list, so for large lists this could be (pointlessly) expensive. A simple extension method to achieve this could be:

<pre><code>public static IEnumerable&lt;TSource&gt; IndexRange&lt;TSource&gt;(
 this IList&lt;TSource&gt; source,
 int fromIndex, 
 int toIndex)
{
 int currIndex = fromIndex;
 while (currIndex &lt;= toIndex)
 {
 yield return source[currIndex];
 currIndex++;
 }
}
</code></pre>

blocks|key|1521146|text|您可以使用GetRange()|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1521147|list.GetRange(index,+count);|code-block|syntax|javascript|1521148|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can use GetRange()

<pre><code>list.GetRange(index, count);
</code></pre>

blocks|key|1306171|text|要按特定索引(而不是从-到)进行筛选：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1306172|public+static+class+ListExtensions
{
+++public+static+IEnumerable<TSource>+ByIndexes<TSource>(this+IList<TSource>+source,+params+int[]+indexes)
+++{++++++++
++++++++if+(indexes+==+null+%7C%7C+indexes.Length+==+0)
++++++++{
++++++++++++foreach+(var+item+in+source)
++++++++++++{
++++++++++++++++yield+return+item;
++++++++++++}
++++++++}
++++++++else
++++++++{
++++++++++++foreach+(var+i+in+indexes)
++++++++++++{
++++++++++++++++if+(i+>=+0+&&+i+<+source.Count)
++++++++++++++++++++yield+return+source[i];
++++++++++++}
++++++++}
+++}
}|code-block|syntax|javascript|1306173|例如：|1306174|string[]+list+=+{"a1",+"b2",+"c3",+"d4",+"e5",+"f6",+"g7",+"h8",+"i9"};
var+filtered+=+list.ByIndexes(5,+8,+100,+3,+2);+//+=+{"f6",+"i9",+"d4",+"c3"};|1306175|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

To filter by specific indexes (not from-to):

<pre><code>public static class ListExtensions
{
 public static IEnumerable&lt;TSource&gt; ByIndexes&lt;TSource&gt;(this IList&lt;TSource&gt; source, params int[] indexes)
 { 
 if (indexes == null || indexes.Length == 0)
 {
 foreach (var item in source)
 {
 yield return item;
 }
 }
 else
 {
 foreach (var i in indexes)
 {
 if (i &gt;= 0 &amp;&amp; i &lt; source.Count)
 yield return source[i];
 }
 }
 }
}
</code></pre>

For example:

<pre><code>string[] list = {"a1", "b2", "c3", "d4", "e5", "f6", "g7", "h8", "i9"};
var filtered = list.ByIndexes(5, 8, 100, 3, 2); // = {"f6", "i9", "d4", "c3"};
</code></pre>

blocks|key|1521266|text|从.NET+6开始，可以使用range+syntax作为Take方法。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1521267|List<int>+intList+=+new+List<int>(new+int[]{1,+2,+3,+3,+2,+1});

//+Starting+from+index+0+(including)+to+index+3+(excluding)+will+select+indexes+(0,+1,+2)
Console.WriteLine(intList.Take(0..3).Sum());+//+{1,+2,+3}+->+6

//+By+default+is+first+index+0+and+can+be+used+following+shortcut.
Console.WriteLine(intList.Take(..3).Sum());++//+{1,+2,+3}+->+6++++++


//+Starting+from+index+3+(including)+to+index+6+(excluding)+will+select+indexes+(3,+4,+5)
Console.WriteLine(intList.Take(3..6).Sum());+//+{3,+2,+1}+->+6++

//+By+default+is+last+index+lent+-1+and+can+be+used+following+shortcut.
Console.WriteLine(intList.Take(3..).Sum());++//+{3,+4,+5}+->+6

//+Reverse+index+syntax+can+be+used.+Take+last+3+items.
Console.WriteLine(intList.Take(%5E3..).Sum());+//+{3,+2,+1}+->+6

//+No+exception+will+be+raised+in+case+of+range+is+exceeded.
Console.WriteLine(intList.Take(%5E100..1000).Sum());+|code-block|syntax|javascript|1521268|所以简单地说，.NET+6可以使用intList.Take(..3).Sum()和intList.Take(3..).Sum()。|style|CODE|1521269|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/tutorials/ranges-indexes^0|E|C|0|0|0|H|N|15|N|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@$A|10|B|11|K|L]|$A|12|B|13|K|L]]|9|@]|C|$]]|$1|M|3|-4|5|6|7|14|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

Starting from .NET 6 it is possible to use <a href="https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/tutorials/ranges-indexes" rel="nofollow noreferrer">range syntax</a> for Take method.
<pre><code>List&lt;int&gt; intList = new List&lt;int&gt;(new int[]{1, 2, 3, 3, 2, 1});

// Starting from index 0 (including) to index 3 (excluding) will select indexes (0, 1, 2)
Console.WriteLine(intList.Take(0..3).Sum()); // {1, 2, 3} -&gt; 6

// By default is first index 0 and can be used following shortcut.
Console.WriteLine(intList.Take(..3).Sum()); // {1, 2, 3} -&gt; 6 


// Starting from index 3 (including) to index 6 (excluding) will select indexes (3, 4, 5)
Console.WriteLine(intList.Take(3..6).Sum()); // {3, 2, 1} -&gt; 6 

// By default is last index lent -1 and can be used following shortcut.
Console.WriteLine(intList.Take(3..).Sum()); // {3, 4, 5} -&gt; 6

// Reverse index syntax can be used. Take last 3 items.
Console.WriteLine(intList.Take(^3..).Sum()); // {3, 2, 1} -&gt; 6

// No exception will be raised in case of range is exceeded.
Console.WriteLine(intList.Take(^100..1000).Sum()); 
</code></pre>
So simply put, <code>intList.Take(..3).Sum()</code> and <code>intList.Take(3..).Sum()</code> can be used with .NET 6.

I am a LINQ newbie trying to use it to acheive the following:

I have a list of ints:-

<pre><code>List&lt;int&gt; intList = new List&lt;int&gt;(new int[]{1,2,3,3,2,1});
</code></pre>

Now, I want to compare the sum of the first three elements [index range 0-2] with the last three [index range 3-5] using LINQ. I tried the LINQ Select and Take extension methods as well as the SelectMany method, but I cannot figure out how to say something like 

<pre><code>(from p in intList 
where p in Take contiguous elements of intList from index x to x+n 
select p).sum()
</code></pre>

I looked at the Contains extension method too, but that doesn't see to get me what I want. Any suggestions? Thanks.

How to select values within a provided index range from a List using LINQ

我是一个LINQ新手，正在尝试使用它来获得以下内容：我有一个int列表：List<int> intList = new List<int>(new int[]{1,2,3,3,2,1});现在，我想使用LINQ比较前三个元素索引范围0-2和后三个索引范围3-5的总和。我尝试了LINQ Select和Take扩展方法以及...

问如何使用LINQ从列表中选择所提供索引范围内的值
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