blocks|key|279315|text|当条件为false时，TakeWhile将停止，Where将继续查找与条件匹配的所有元素|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|279316|var+intList+=+new+int[]+{+1,+2,+3,+4,+5,+-1,+-2+};
Console.WriteLine("Where");
foreach+(var+i+in+intList.Where(x+=>+x+<=+3))
++++Console.WriteLine(i);
Console.WriteLine("TakeWhile");
foreach+(var+i+in+intList.TakeWhile(x+=>+x+<=+3))
++++Console.WriteLine(i);|code-block|syntax|javascript|279317|给出|279318|Where
1
2
3
-1
-2
TakeWhile
1
2
3|279319|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.takewhile?view=netcore-3.1|1|https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.where?view=netcore-3.1^0|B|9|O|5|B|9|0|O|5|1|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@$9|13|A|14|1|15]|$9|16|A|17|1|18]]|E|$]]|$1|F|3|G|5|H|7|19|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1A|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|1B|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|1C|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]|W|$5|R|S|T|E|$U|X]]]]

<a href="https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.takewhile?view=netcore-3.1" rel="noreferrer"><code>TakeWhile</code></a> stops when the condition is false, <a href="https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.where?view=netcore-3.1" rel="noreferrer"><code>Where</code></a> continues and find all elements matching the condition
<pre><code>var intList = new int[] { 1, 2, 3, 4, 5, -1, -2 };
Console.WriteLine(&quot;Where&quot;);
foreach (var i in intList.Where(x =&gt; x &lt;= 3))
 Console.WriteLine(i);
Console.WriteLine(&quot;TakeWhile&quot;);
foreach (var i in intList.TakeWhile(x =&gt; x &lt;= 3))
 Console.WriteLine(i);
</code></pre>
Gives
<pre><code>Where
1
2
3
-1
-2
TakeWhile
1
2
3
</code></pre>

blocks|key|3202215|text|Where可以检查整个序列以查找匹配项。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3202216|Enumerable.Range(1,+10).Where(x+=>+x+%25+2+==+1)
//+1,+3,+5,+7,+9|code-block|syntax|javascript|3202217|当遇到第一个不匹配时，TakeWhile将停止查找。|3202218|Enumerable.Range(1,+10).TakeWhile(x+=>+x+%25+2+==+1)
//+1|3202219|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.where?view=netcore-3.1|1|https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.takewhile?view=netcore-3.1^0|0|5|0|5|0|0|0|B|9|B|9|1|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]]|D|@$9|11|A|12|1|13]]|E|$]]|$1|F|3|G|5|H|7|14|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|15|8|@$9|16|A|17|B|C]]|D|@$9|18|A|19|1|1A]]|E|$]]|$1|M|3|N|5|H|7|1B|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|1C|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]|W|$5|R|S|T|E|$U|X]]]]

<a href="https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.where?view=netcore-3.1" rel="nofollow noreferrer"><code>Where</code></a> can examine the whole sequence looking for matches.
<pre><code>Enumerable.Range(1, 10).Where(x =&gt; x % 2 == 1)
// 1, 3, 5, 7, 9
</code></pre>
<a href="https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.takewhile?view=netcore-3.1" rel="nofollow noreferrer"><code>TakeWhile</code></a> stops looking when it encounters the first non-match.
<pre><code>Enumerable.Range(1, 10).TakeWhile(x =&gt; x % 2 == 1)
// 1
</code></pre>

blocks|key|3202260|text|假设您有一个包含[1,+3,+5,+7,+9,+0,+2,+4,+6,+8]的数组。现在：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3202261|var+whereTest+=+array.Where(i+=>+i+<=+5);将返回[1,+3,+5,+0,+2,+4]。|3202262|var+whileTest+=+array.TakeWhile(i+=>+i+<=+5);将返回[1,+3,+5]。|3202263|entityMap^0|8|U|0|0|15|18|I|0|0|19|1C|9|0^^$0|@$1|2|3|4|5|6|7|L|8|@$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|T|8|@$9|U|A|V|B|C]|$9|W|A|X|B|C]]|D|@]|E|$]]|$1|J|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|K|$]]

Say you have an array that contains <code>[1, 3, 5, 7, 9, 0, 2, 4, 6, 8]</code>. Now:

<code>var whereTest = array.Where(i =&gt; i &lt;= 5);</code> will return <code>[1, 3, 5, 0, 2, 4]</code>.

<code>var whileTest = array.TakeWhile(i =&gt; i &lt;= 5);</code> will return <code>[1, 3, 5]</code>.

blocks|key|3202302|text|MSDN说|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3202303|Enumerable.TakeWhile+Method|offset|length|style|CODE|3202304|只要指定的条件为真，|3202305|就返回序列中的元素，然后跳过其余的元素。|blockquote|3202306|3202307|3202308|Enumerable.Where|3202309|3202310|根据谓词过滤一系列值。|3202311|3202312|3202313|不同之处在于，Enumerable.TakeWhile+将跳过第一个不匹配中的其余元素，无论它们是否与条件匹配|BOLD|3202314|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/system.linq.enumerable.takewhile.aspx|1|http://msdn.microsoft.com/en-us/library/bb534803.aspx^0|0|0|R|0|R|0|0|0|0|0|0|0|G|0|G|1|0|0|0|0|0|7|K|S|R|0^^$0|@$1|2|3|4|5|6|7|18|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|19|8|@$D|1A|E|1B|F|G]]|9|@$D|1C|E|1D|1|1E]]|A|$]]|$1|H|3|I|5|6|7|1F|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|1G|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|1H|8|@]|9|@]|A|$]]|$1|N|3|-4|5|6|7|1I|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|1J|8|@$D|1K|E|1L|F|G]]|9|@$D|1M|E|1N|1|1O]]|A|$]]|$1|Q|3|-4|5|6|7|1P|8|@]|9|@]|A|$]]|$1|R|3|S|5|L|7|1Q|8|@]|9|@]|A|$]]|$1|T|3|-4|5|6|7|1R|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|1S|8|@]|9|@]|A|$]]|$1|V|3|W|5|6|7|1T|8|@$D|1U|E|1V|F|G]|$D|1W|E|1X|F|X]]|9|@]|A|$]]|$1|Y|3|-4|5|6|7|1Y|8|@]|9|@]|A|$]]]|Z|$10|$5|11|12|13|A|$14|15]]|16|$5|11|12|13|A|$14|17]]]]

MSDN says

<a href="http://msdn.microsoft.com/en-us/library/system.linq.enumerable.takewhile.aspx" rel="noreferrer"><code>Enumerable.TakeWhile Method</code></a>

<blockquote>
 Returns elements from a sequence as
 long as a specified condition is true,
 and then skips the remaining elements.
</blockquote>

<a href="http://msdn.microsoft.com/en-us/library/bb534803.aspx" rel="noreferrer"><code>Enumerable.Where</code></a>

<blockquote>
 Filters a sequence of values based on
 a predicate.
</blockquote>

The difference is that <code>Enumerable.TakeWhile</code> skips the remaining elements from the first non-match whether they match the condition or not

blocks|key|279367|text|虽然现有的答案是正确的，但没有一个答案指出，如果结果是相同的，为什么要使用+TakeWhile+:+Performance。假设您有一个包含20亿项的有序列表，并且您想要小于给定值的项(可能是10项或15项)。Where子句将检查所有20亿个项目，而TakeWhile将在发现一个等于或大于您提供的值的值时立即停止|type|unstyled|depth|inlineStyleRanges|entityRanges|data|279368|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

While the existing answers are correct, none of them point out why you'd want to use TakeWhile if the results would be the same: Performance. Suppose you have an ordered list with 2 billion items in it, and you want the ones that (probably 10 or 15 items) less than a given vallue. The Where clause will examine all 2 billion items, while the TakeWhile will stop as soon as it finds a value equal or greater than your supplied value

blocks|key|277644|text|对于TakeWhile，传递的序列的顺序是绝对关键的，一旦谓词返回false，它就会终止，而Where将在第一个false值之后继续计算序列。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|277645|TakeWhile的一种常见用法是在对大型、昂贵甚至无限的可枚举数进行惰性计算期间，您可能对序列的排序有更多的了解。|277646|例如，给定序列：|277647|IEnumerable<BigInteger>+InfiniteSequence()
{
++++BigInteger+sequence+=+0;
++++while+(true)
++++{
++++++++yield+return+sequence%2B%2B;
++++}
}|code-block|syntax|javascript|277648|.Where将导致无限循环，试图计算可枚举数的一部分：|277649|var+result+=+InfiniteSequence()
++++.Where(n+=>+n+<+100)
++++.Count();|277650|然而，在知道可枚举数是递增的情况下，.TakeWhile将允许评估部分序列：|277651|var+result+=+InfiniteSequence()
++++.TakeWhile(n+=>+n+<+100)
++++.Count();|277652|entityMap^0|2|9|X|5|1A|5|1K|5|0|0|9|0|0|0|0|6|0|0|I|A|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|1A|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|1B|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|1C|8|@$9|1D|A|1E|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|L|7|1F|8|@]|D|@]|E|$M|N]]|$1|S|3|T|5|6|7|1G|8|@$9|1H|A|1I|B|C]]|D|@]|E|$]]|$1|U|3|V|5|L|7|1J|8|@]|D|@]|E|$M|N]]|$1|W|3|-4|5|6|7|1K|8|@]|D|@]|E|$]]]|X|$]]

The order of the sequence passed is absolutely critical with <code>TakeWhile</code>, which will terminate as soon as a predicate returns <code>false</code>, whereas <code>Where</code> will continue to evaluate the sequence beyond the first <code>false</code> value.

A common usage for <code>TakeWhile</code> is during the lazy evaluation of large, expensive, or even infinite enumerables where you may have additional knowledge about the ordering of the sequence. 

e.g. Given the sequence:

<pre><code>IEnumerable&lt;BigInteger&gt; InfiniteSequence()
{
 BigInteger sequence = 0;
 while (true)
 {
 yield return sequence++;
 }
}
</code></pre>

A <code>.Where</code> will result in an infinite loop trying to evaluate part of the enumerable:

<pre><code>var result = InfiniteSequence()
 .Where(n =&gt; n &lt; 100)
 .Count();
</code></pre>

Whereas a <code>.TakeWhile</code>, and armed with the knowledge that the enumerables is ascending, will allow the partial sequence to be evaluated:

<pre><code>var result = InfiniteSequence()
 .TakeWhile(n =&gt; n &lt; 100)
 .Count();
</code></pre>

I want to get a difference between <a href="https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.takewhile?view=netcore-3.1" rel="noreferrer"><code>TakeWhile</code></a> &amp; <a href="https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.where?view=netcore-3.1" rel="noreferrer"><code>Where</code></a> LINQ methods .I got the following data from MSDN .But It didn't make sense to me
<blockquote>
<pre><code>Where&lt;TSource&gt;(IEnumerable&lt;TSource&gt;, Func&lt;TSource, Boolean&gt;) 
</code></pre>
Filters a sequence of values based on a predicate.
</blockquote>
<blockquote>
<pre><code>TakeWhile&lt;TSource&gt;(IEnumerable&lt;TSource&gt;, Func&lt;TSource, Boolean&gt;)
</code></pre>
Returns elements from a sequence as long as a specified condition is true.
</blockquote>
All opinions are welcomed.

LINQ where vs takewhile

我想知道和 LINQ方法之间的区别.I从MSDN .But得到了以下数据，这对我来说没有意义 Where(IEnumerable、Func<TSource、Boolean>)根据谓词筛选一系列值。TakeWhile(IEnumerable、Func<TSource、Boolean>)只要指定的条件为真，就返回序列中的元素。欢迎所有的意见。

问LINQ where vs takewhile
EN

回答 6

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问LINQ where vs takewhile
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