LINQ:从列表中选择项目(分组依据/选择/总和最大！) [英] LINQ: Selecting items from a list (Group By/Select/Sum & Max!)

问题描述

让我绕着Linq前进，玩得开心！有人可以帮我查询一下吗?
我有一个数据列表:

Just getting my head around Linq and having lots of fun! Can any one aid me with a query for this:
I have a list of data:

    Key  Value
    Aaa  12
    AaA  10
    AAa  5
    BBB  2
    Bbb  1

1.我想按Key.ToUpper()分组
2.对于每个组，我都需要Max(Value)&总和(值)
3.对于每个组，我要选择条目出现值！=最大值(值)
最终结果应如下所示:

1. I want to group by Key.ToUpper()
2. For every group I need the Max(Value) & Sum(Value)
3. For every group I want to select the entries There the Value != Max(value)
the final result should be like this:

    Key Max Total
    AaA 12  27
    AAa 12  27
    Bbb 2   3

谢谢！

更新，实际上我还需要最大"条目中的密钥":

Update, actually I also need the Key from the Maximum entry:

    Key Max Total Correct
    AaA 12  27    Aaa
    AAa 12  27    Aaa
    Bbb 2   3     BBB 

推荐答案

:)

var results =
  from kvp in source
  group kvp by kvp.Key.ToUpper() into g
  select new
  {
    Group = g,
    Max = g.Max(kvp => kvp.Value),
    Total = g.Sum(kvp => kvp.Value)
  } into ag
  from x in ag.Group  //SelectMany
  where x.Value != ag.Max
    //for the update to the question - note: possibly ambiguous
  let correct = ag.Group.Where(y => y.Value == ag.Max).First().Key
  select new
  {
    Key = x.Key,
    Max = ag.Max,
    Total = ag.Total,
    Correct = correct 
  };

我有点喜欢这个问题，因为所有小部分(很少使用)都需要答案.

I kinda like the question because of all the little parts (some are rarely used) that are required to make the answer.

Max = g.Max(kvp => kvp.Value),
Total = g.Sum(kvp => kvp.Value)

在一个组上执行多个聚合非常简单，但是如果您不知道如何的话就很困难.

Performing multiple aggregations on a group is straightforward, yet challenging if you don't know how.

select a into b

此子句采用之前发生的所有事情，并使用目标启动新查询.没有它，我将不得不像这样开始一个新的查询:

This clause takes everything that happened before and starts a new query with the target. Without it, I'd have to start a new query like this:

var A = ... select a

var B = from b in A

请注意， select into 子句将从范围中删除 kvp 和 g .

It's important to note that the select into clause removes kvp and g from scope.

  from b in source
  from a in b.A  //SelectMany

此子集合的拆包"将我对b的查询转换为对a的查询.与默认的Enumerable.SelectMany重载不同，它将父级( b )保留在范围内.

This "unpacking" of the child collection turns my query about b's into a query about a's. Unlike the default Enumerable.SelectMany overload, it leaves the parent (b) in scope.

where x.Value != ag.Max

将孩子的财产与父母的财产进行比较?愉快.重要的是要记住，即使您刚刚分组(没有 HAVING )，也要在要过滤的任何时间打破 where .

Comparing a child's property with a parent's property? Delightful. It's important to remember to break out where anytime you want to filter, even if you just grouped (there is no HAVING).

这篇关于LINQ:从列表中选择项目(分组依据/选择/总和最大！)的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！