Linq查询选择顶级记录

Question

我有IEnumerable<MyData> ，其中包含以下数据

Fruits | Name | Quantity | 
__________________________
 Mango | Jay  |    10    |
__________________________
 Apple | Jay  |    16    |
__________________________
 Grapes| Jay  |    12    |
__________________________
 Mango | Raj  |    11    |
__________________________
 Apple | Raj  |    20    |
__________________________
 Grapes| Raj  |    3     |
__________________________
 Mango | Vik  |    20    |
__________________________
 Apple | Vik  |    15    |
__________________________

我需要根据名称从Linq顶部选择两个数量

Jay (10+16+12) = 38
Raj (11+20+3) = 34
Vik (20+15) = 35

Jay和Vik有两个数量之和，所以我需要这些记录

Fruits | Name | Quantity | 
__________________________
 Mango | Jay  |    10    |
__________________________
 Apple | Jay  |    16    |
__________________________
 Grapes| Jay  |    12    |
__________________________
 Mango | Vik  |    20    |
__________________________
 Apple | Vik  |    15    |
__________________________

Answer 1

听起来像你可能想要的东西：

var query = from item in collection
            group item by item.Name into g
            orderby g.Sum(x => x.Quantity)  descending
            select g;
var topTwo = query.Take(2);

这将采用前两组 ，因此您将其用作：

foreach (var group in topTwo)
{
    Console.WriteLine("Name: {0}", group.Key);
    foreach (var item in group)
    {
        Console.WriteLine("  {0}: {1}", item.Fruits, item.Quantity);
    }
}

Answer 2

像这样的东西会起作用。

private static IEnumerable<MyData> GetTop2Names(IEnumerable<MyData> data)
{
    var top2 = data.GroupBy(d => d.Name)
                   .OrderByDescending(g => g.Sum(d => d.Quantity))
                   .Take(2)
                   .Select(g => g.Key);
    return data.Where(d => top2.Contains(d.Name));
}

一步步

1. 按名称分组（因为这就是你的总结）
2. 按数量之和排序
3. 取前2名
4. 从原始列表中选择与这些名称匹配的项目。

Answer 3

请尝试以下方法：

var topTwo = myData.GroupBy(d => d.Name).OrderByDescending(g => g.Sum(d => d.Quantity)).TakeWhile((data,index) => index < 2).SelectMany(g => g);

Answer 4

应该是这样的：

IEnumerable<MyData> source = new List<MyData>();
var names = source
    .GroupBy(item => item.Name)
    .ToDictionary(item => item.Key, item => item.Sum(i => i.Quantity))
    .OrderByDescending(item => item.Value)
    .Select(item => item.Key)
    .Take(2);

var result = source.Where(item => names.Contains(item.Name));