blocks|key|5101091|text|我认为以下几点应该是可行的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5101092|List<MyTable>+items+=+GetItems();
var+orderedByMax+=+from+i+in+items
+++++++++++++++++++group+i+by+i.Date+into+g
+++++++++++++++++++let+q+=+g.GroupBy(i+=>+i.Range)
++++++++++++++++++++++++++++.Select(g2+=>+new+{Range+=+g2.Key,+Count+=+g2.Count()})
++++++++++++++++++++++++++++.OrderByDescending(i+=>+i.Count)
+++++++++++++++++++let+max+=+q.FirstOrDefault()
+++++++++++++++++++select+new+{
++++++++++++++++++++++Date+=+g.Key,
++++++++++++++++++++++Range+=+max.Range,
++++++++++++++++++++++Total+=+max.Count
+++++++++++++++++++};|code-block|syntax|javascript|5101093|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|$]]

I think something along these lines should work:

<pre><code>List&lt;MyTable&gt; items = GetItems();
var orderedByMax = from i in items
 group i by i.Date into g
 let q = g.GroupBy(i =&gt; i.Range)
 .Select(g2 =&gt; new {Range = g2.Key, Count = g2.Count()})
 .OrderByDescending(i =&gt; i.Count)
 let max = q.FirstOrDefault()
 select new {
 Date = g.Key,
 Range = max.Range,
 Total = max.Count
 };
</code></pre>

blocks|key|201564|text|使用扩展方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|201565|List<MyTable>+items+=+GetItems();

var+rangeTotals+=+items.GroupBy(x+=>+new+{+x.Date,+x.Range+})+//+Group+by+Date+%2B+Range
++++++++++++++++++.Select(g+=>+new+{+
++++++++++++++++++++++++++++++Date+=+g.Key.Date,+
++++++++++++++++++++++++++++++Range+=+g.Key.Range,+
++++++++++++++++++++++++++++++Total+=+g.Count()+//+Count+total+of+identical+ranges+per+date
++++++++++++++++++++++++++++++});

var+rangeMaxTotals+=+rangeTotals.Where(rt+=>+!rangeTotals.Any(z+=>+z.Date+==+rt.Date+&&+z.Total+>+rt.Total));+//+Get+maximum+totals+for+each+date|code-block|syntax|javascript|201566|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|$]]

Using extension methods:

<pre><code>List&lt;MyTable&gt; items = GetItems();

var rangeTotals = items.GroupBy(x =&gt; new { x.Date, x.Range }) // Group by Date + Range
 .Select(g =&gt; new { 
 Date = g.Key.Date, 
 Range = g.Key.Range, 
 Total = g.Count() // Count total of identical ranges per date
 });

var rangeMaxTotals = rangeTotals.Where(rt =&gt; !rangeTotals.Any(z =&gt; z.Date == rt.Date &amp;&amp; z.Total &gt; rt.Total)); // Get maximum totals for each date
</code></pre>

blocks|key|5101071|text|不幸的是，我现在不能测试它，但试一试：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5101072|List<MyTable>+items+=+GetItems();
items.Max(t=>t.Range.Distinct().Count());|code-block|syntax|javascript|5101073|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|$]]

unfortunately I can't test this at the moment but give this a try:

<pre><code>List&lt;MyTable&gt; items = GetItems();
items.Max(t=&gt;t.Range.Distinct().Count());
</code></pre>

blocks|key|2986976|text|这种方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2986977|1)按日期分组|2986978|2)对于每个日期，按范围分组并计算合计|2986979|3)对于每个日期，选择合计最大的项目|2986980|4)你最终得到你的结果|2986981|public+sealed+class+Program
{
++++public+static+void+Main(string[]+args)
++++{
++++++++var+items+=+new[]
++++++++{
++++++++++++new+{+ID+=+1,+Date+=+new+DateTime(10,+10,+10),+Range+=+"9-10"+},
++++++++++++new+{+ID+=+2,+Date+=+new+DateTime(10,+10,+10),+Range+=+"9-10"+},
++++++++++++new+{+ID+=+3,+Date+=+new+DateTime(10,+10,+10),+Range+=+"9-10"+},
++++++++++++new+{+ID+=+4,+Date+=+new+DateTime(10,+10,+10),+Range+=+"8-9"+},
++++++++++++new+{+ID+=+5,+Date+=+new+DateTime(10,+10,+11),+Range+=+"1-2"+},
++++++++++++new+{+ID+=+6,+Date+=+new+DateTime(10,+10,+11),+Range+=+"1-2"+},
++++++++++++new+{+ID+=+7,+Date+=+new+DateTime(10,+10,+12),+Range+=+"5-6"+},
++++++++};

++++++++var+itemsWithTotals+=+items
++++++++++++.GroupBy(item+=>+item.Date)++//+Group+by+Date.
++++++++++++.Select(groupByDate+=>+groupByDate
++++++++++++++++.GroupBy(item+=>+item.Range)++//+Group+by+Range.
++++++++++++++++.Select(groupByRange+=>+new
++++++++++++++++{
++++++++++++++++++++Date+=+groupByDate.Key,
++++++++++++++++++++Range+=+groupByRange.Key,
++++++++++++++++++++Total+=+groupByRange.Count()
++++++++++++++++})++//+Got+the+totals+for+each+grouping.
++++++++++++++++.MaxElement(item+=>+item.Total));++//+For+each+Date,+grab+the+item+(grouped+by+Range)+with+the+greatest+Total.

++++++++foreach+(var+item+in+itemsWithTotals)
++++++++++++Console.WriteLine("{0}+{1}+{2}",+item.Date.ToShortDateString(),+item.Range,+item.Total);

++++++++Console.Read();
++++}
}

///+<summary>
///+From+the+book+LINQ+in+Action,+Listing+5.35.
///+</summary>
static+class+ExtensionMethods
{
++++public+static+TElement+MaxElement<TElement,+TData>(this+IEnumerable<TElement>+source,+Func<TElement,+TData>+selector)+where+TData+:+IComparable<TData>
++++{
++++++++if+(source+==+null)
++++++++++++throw+new+ArgumentNullException("source");
++++++++if+(selector+==+null)
++++++++++++throw+new+ArgumentNullException("selector");

++++++++bool+firstElement+=+true;
++++++++TElement+result+=+default(TElement);
++++++++TData+maxValue+=+default(TData);
++++++++foreach+(TElement+element+in+source)
++++++++{
++++++++++++var+candidate+=+selector(element);
++++++++++++if+(firstElement+%7C%7C+(candidate.CompareTo(maxValue)+>+0))
++++++++++++{
++++++++++++++++firstElement+=+false;
++++++++++++++++maxValue+=+candidate;
++++++++++++++++result+=+element;
++++++++++++}
++++++++}
++++++++return+result;
++++}
}|code-block|syntax|javascript|2986982|根据LINQ+in+Action+(第5.3.3章-+LINQ+to+Objects是否会损害代码的性能？)，使用MaxElement扩展方法是最有效的方法之一。我认为性能将是O(4n)；一个用于第一个GroupBy，两个用于第二个计数，三个用于GroupBy()，四个用于MaxElement内的循环。|2986983|DrDro的方法将更像O(n%5E2)，因为它为列表中的每一项循环整个列表。|2986984|StriplingWarrior的方法将更接近O(n+log+n)，因为它对项进行排序。尽管我承认，这里面可能有一些我不理解的疯狂的魔法。|2986985|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Y|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|Z|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|10|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|11|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|12|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|13|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|14|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|V|$]]

This approach: 
1) Groups by Date 
2) For each Date, groups by Range and calculates the Total 
3) For each Date, selects the item with the greatest Total 
4) You end up with your result

<pre><code>public sealed class Program
{
 public static void Main(string[] args)
 {
 var items = new[]
 {
 new { ID = 1, Date = new DateTime(10, 10, 10), Range = "9-10" },
 new { ID = 2, Date = new DateTime(10, 10, 10), Range = "9-10" },
 new { ID = 3, Date = new DateTime(10, 10, 10), Range = "9-10" },
 new { ID = 4, Date = new DateTime(10, 10, 10), Range = "8-9" },
 new { ID = 5, Date = new DateTime(10, 10, 11), Range = "1-2" },
 new { ID = 6, Date = new DateTime(10, 10, 11), Range = "1-2" },
 new { ID = 7, Date = new DateTime(10, 10, 12), Range = "5-6" },
 };

 var itemsWithTotals = items
 .GroupBy(item =&gt; item.Date) // Group by Date.
 .Select(groupByDate =&gt; groupByDate
 .GroupBy(item =&gt; item.Range) // Group by Range.
 .Select(groupByRange =&gt; new
 {
 Date = groupByDate.Key,
 Range = groupByRange.Key,
 Total = groupByRange.Count()
 }) // Got the totals for each grouping.
 .MaxElement(item =&gt; item.Total)); // For each Date, grab the item (grouped by Range) with the greatest Total.

 foreach (var item in itemsWithTotals)
 Console.WriteLine("{0} {1} {2}", item.Date.ToShortDateString(), item.Range, item.Total);

 Console.Read();
 }
}

/// &lt;summary&gt;
/// From the book LINQ in Action, Listing 5.35.
/// &lt;/summary&gt;
static class ExtensionMethods
{
 public static TElement MaxElement&lt;TElement, TData&gt;(this IEnumerable&lt;TElement&gt; source, Func&lt;TElement, TData&gt; selector) where TData : IComparable&lt;TData&gt;
 {
 if (source == null)
 throw new ArgumentNullException("source");
 if (selector == null)
 throw new ArgumentNullException("selector");

 bool firstElement = true;
 TElement result = default(TElement);
 TData maxValue = default(TData);
 foreach (TElement element in source)
 {
 var candidate = selector(element);
 if (firstElement || (candidate.CompareTo(maxValue) &gt; 0))
 {
 firstElement = false;
 maxValue = candidate;
 result = element;
 }
 }
 return result;
 }
}
</code></pre>

According to LINQ in Action (Chapter 5.3.3 - Will LINQ to Objects hurt the performance of my code?), using the MaxElement extension method is one of the most effecient approaches. I think the performance would be O(4n); one for the first GroupBy, two for the second GroupBy, three for the Count(), and four for loop within MaxElement.

DrDro's approach is going to be more like O(n^2) since it loops the entire list for each item in the list.

StriplingWarrior's approach is going to be closer to O(n log n) because it sorts the items. Though I'll admit, there may be some crazy magic in there that I don't understand.

I'm new to LINQ and I have this situation. I have this table:

<pre><code>ID Date Range
1 10/10/10 9-10
2 10/10/10 9-10
3 10/10/10 9-10
4 10/10/10 8-9
5 10/11/10 1-2
6 10/11/10 1-2
7 10/12/10 5-6
</code></pre>

I just want to list the Maximun of rows per date by range, like this:

<pre><code>Date Range Total
10/10/10 9-10 3
10/11/10 1-2 2
10/12/10 5-6 1
</code></pre>

I want to do this by using LINQ, do you have any ideas of how to do this?

How to get the Max() of a Count() with LINQ

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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我是LINQ的新手，我遇到了这种情况。我有一张桌子：ID Date  Range1 10/10/10 9-102 10/10/10 9-103 10/10/10 9-104 10/10/10 8-95 10/11/10 1-26 10/11/10 1-27 10/12/10 5-6我只想按范围列出每个日期的最大行数，如下所示：Date  Range  Total10/10/10 9-10  310

问如何使用LINQ获取Count()的Max()
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问如何使用LINQ获取Count()的Max()
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