Linq选择不同的值与比较

Question

我有一个对象列表。例如List<coin>，其中它们包含字符串(dom)和int(year)。如果列表包含:

"Quarter", 1954
"Quarter", 1990
"Penny", 1925  
"Nickel", 1900 
"Nickel", 2000

我怎样才能得到一个结果列表，其中包含最近一年的唯一值?例如:

"Quarter", 1990
"Penny", 1925
"Nickel", 2000

Answer 1

您可以通过按名称分组，然后排序并获取第一个结果，或者使用MoreLINQ:

中的MaxBy来实现这一点

var query = coins.GroupBy(x => x.Name)
                 .Select(g => g.MaxBy(x => x.Year));

或

var query = coins.GroupBy(x => x.Name)
                 .Select(g => g.OrderByDescending(x => x.Year).First());

Answer 2

您可以使用group by这样做:

 var query = from coin in myList
        group coin by coin.Name into grouped
        select new
        {
            Name = grouped.Key
            Year = grouped.Max(x => x.Year) 
        };

另一个类似的示例，查看101 Linq示例中的"max - grouped": http://msdn.microsoft.com/en-us/vcsharp/aa336747#maxGrouped

Answer 3

var coins = new Coin[] { ... };
var recentCoins =
    from coin in coins
    group coin by coin.Denom into g
    select new
    {
        Denom = g.Key, 
        MostRecentYear = g.Max(c => c.Year)
    };