select的源码public static IEnumerable<TResult> Select<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TResult> selector);
class Program
{
static void Main(string[] args)
{
var customers = new[] {
new { CustomerID = 1, FirstName = "Orlando", LastName = "Gee",
CompanyName = "A Bike Store" },
new { CustomerID = 2, FirstName = "Keith", LastName = "Harris",
CompanyName = "Bike World" },
new { CustomerID = 3, FirstName = "Donna", LastName = "Carreras",
CompanyName = "A Bike Store" },
new { CustomerID = 4, FirstName = "Janet", LastName = "Gates",
CompanyName = "Fitness Hotel" },
new { CustomerID = 5, FirstName = "Lucy", LastName = "Harrington",
CompanyName = "Grand Industries" },
new { CustomerID = 6, FirstName = "David", LastName = "Liu",
CompanyName = "Bike World" },
new { CustomerID = 7, FirstName = "Donald", LastName = "Blanton",
CompanyName = "Grand Industries" },
new { CustomerID = 8, FirstName = "Jackie", LastName = "Blackwell",
CompanyName = "Fitness Hotel" },
new { CustomerID = 9, FirstName = "Elsa", LastName = "Leavitt",
CompanyName = "Grand Industries" },
new { CustomerID = 10, FirstName = "Eric", LastName = "Lang",
CompanyName = "Distant Inn" }
};
var addresses = new[] {
new { CompanyName = "A Bike Store", City = "New York", Country = "United States"},
new { CompanyName = "Bike World", City = "Chicago", Country = "United States"},
new { CompanyName = "Fitness Hotel", City = "Ottawa", Country = "Canada"},
new { CompanyName = "Grand Industries", City = "London",Country = "United Kingdom"},
new { CompanyName = "Distant Inn", City = "Tetbury", Country = "United Kingdom"}
};
//查询数据
IEnumerable<string> customerFirstNames = customers.Select(cust => cust.FirstName);
//IEnumerable<string> customerFirstNames = from custs in customers select custs.FirstName;
foreach (string name in customerFirstNames)
{
Console.WriteLine(name);
}
Console.WriteLine(" ");
IEnumerable<string> customerFullNames = customers.Select(cust => cust.FirstName + " " + cust.LastName);
//IEnumerable<string> customerFullNames = from custs in customers select custs.FirstName + " " + custs.LastName;
foreach (string name in customerFullNames)
{
Console.WriteLine(name);
}
Console.WriteLine(" ");
var customerNames = customers.Select(cust => new { FirstName = cust.FirstName, LastName = cust.LastName });
//var customerNames = from custs in customers select new { FirstName = custs.FirstName, LastName = custs.LastName };
foreach (var name in customerNames)
{
Console.WriteLine(name);
}
//数据筛选
Console.WriteLine(" ");
IEnumerable<string> usCompanies = addresses.Where(addr => String.Equals(addr.Country, "United States"))
.Select(usComp => usComp.CompanyName);
//IEnumerable<string> usCompanies = from adr in addresses
// where String.Equals(adr.Country, "United States")
// select adr.CompanyName;
foreach (string name in usCompanies)
{
Console.WriteLine(name);
}
//数据排序
Console.WriteLine(" ");
IEnumerable<string> companyNames = addresses.OrderBy(addr => addr.CompanyName).Select(comp => comp.CompanyName);
//IEnumerable<string> companyNames = from adr in addresses orderby adr.CompanyName select adr.CompanyName;
foreach (string name in companyNames)
{
Console.WriteLine(name);
}
Console.WriteLine(" ");
//数据分组---分组之后变成二维数组
var companiesGroupedByCountry = addresses.GroupBy(addrs => addrs.Country);
//var companiesGroupedByCountry = from adr in addresses group adr by adr.Country;
foreach (var companiesPerCountry in companiesGroupedByCountry)
{
Console.WriteLine("Country: {0} {1} companies",
companiesPerCountry.Key, companiesPerCountry.Count());
foreach (var companies in companiesPerCountry)
{
Console.WriteLine(" {0}", companies.CompanyName);
}
}
//数据统计
Console.WriteLine(" ");
int numberOfCountries = addresses.Select(addr => addr.Country).Distinct().Count();
//int numberOfCountries = (from adr in addresses select adr.Country).Distinct().Count();
Console.WriteLine("Number of countries: {0}", numberOfCountries);
//联合查询--内联查询
Console.WriteLine(" ");
var citiesAndCustomers = customers.Select(c =>
new { c.FirstName, c.LastName, c.CompanyName })
.Join(addresses, custs => custs.CompanyName, addrs => addrs.CompanyName, (custs, addrs) => new { custs.FirstName, custs.LastName, addrs.Country });
//var citiesAndCustomers = from cuts in customers
// join adr in addresses
// on cuts.CompanyName equals adr.CompanyName
// select new { cuts.FirstName, cuts.LastName, adr.Country };
foreach (var row in citiesAndCustomers)
{
Console.WriteLine(row);
}
Console.ReadKey();
}
}
}private static void Orderby()
{
int[] intAry1 = { 4, 3, 556, 34, 6, 2, 67 };
var query1 = from var1 in intAry1
orderby var1 ascending
select var1;
query1.ToList().ForEach(p => Console.Write(p + Environment.NewLine));
var query2 = from var1 in intAry1
orderby var1 descending
select var1;
query2.ToList().ForEach(p => Console.Write(p + Environment.NewLine));
Console.WriteLine();
}private static void Join左外部连接()
{
int[] intAry1 = { 5, 15, 25, 30, 33, 40 };
int[] intAry2 = { 5, 20, 30, 30, 50, 70, 80 };
var query1 = from var1 in intAry1
join var2 in intAry2 on var1 equals var2 into var2Grp //左连接 右连接相反
from grp in var2Grp.DefaultIfEmpty()
select new { a = var1 != 0 ? var1 : 100, b = grp };
query1.ToList().ForEach(p => Console.Write("{0}:{1}", p.a, p.b + Environment.NewLine));
Console.WriteLine();
}private static void Join分组连接()
{
int[] intAry1 = { 5, 15, 25, 30, 33, 40 };
int[] intAry2 = { 5, 20, 30, 30, 50, 70, 80 };
var query1 = from var1 in intAry1
join var2 in intAry2 on var1 equals var2 into var2Grp
select new { a = var1, b = var2Grp };
foreach (var item in query1)
{
Console.Write("{0}:", item.a);
foreach (var o in item.b)
{
Console.Write("{0} ", o);
}
Console.WriteLine();
}
Console.WriteLine();
}private static void Join内部连接()
{
int[] intAry1 = { 5, 15, 25, 30, 33, 40 };
int[] intAry2 = { 5, 20, 30, 30, 50, 70, 80 };
var query1 = from var1 in intAry1
join var2 in intAry2 on var1 equals var2
select new { a = var1, b = var2 };
query1.ToList().ForEach(p => Console.Write(p.a + Environment.NewLine));
Console.WriteLine();
}