1. 类型筛选
object[] data = { "one", 2, 4, "Four", "five", 6 };
var query = data.OfType<string>();
foreach (var s in query)
{
Console.WriteLine(s);
}
输出： "one", "Four", "five"
2. 复合查询
var ferrariDrivers = from r in Formula1.GetChampions()
from c in r.Cars
where c == "Ferrari"
orderby r.LastName
select r.FirstName + " " + r.LastName;
使用方法的复合查询
var ferrariDrivers = Formula1.GetChampions()
.SelectMany(r => r.Cars, (r, c) => new { Racer = r, Car = c })
.Where(r => r.Car == "Ferrari")
.OrderBy(r => r.Racer.LastName)
.Select(r => r.Racer.FirstName + " " + r.Racer.LastName);
3. 分组
var countries = from r in Formula1.GetChampions()
group r by r.Country into g
orderby g.Count() descending, g.Key
where g.Count() >= 2
select new
{
Country = g.Key,
count = g.Count()
};
使用方法分组
var countries = Formula1.GetChampions()
.GroupBy(r => r.Country)
.OrderByDescending(g => g.Count())
.ThenBy(g => g.Key)
.Where(g => g.Count() >= 2)
.Select(g => new
{
Country = g.Key,
count = g.Count()
});
嵌套对象的分组
var countries = from r in Formula1.GetChampions()
group r by r.Country into g
let count = g.Count()
orderby count descending, g.Key
where count >= 2
select new
{
Country = g.Key,
Count = count,
Racers = from r1 in g
orderby r1.LastName
select r1.FirstName + " " + r1.LastName
};
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