学步园

Count - Simple

This sample uses Count to get the number of unique factors of 300.

public void Linq73()
{
    int[] factorsOf300 = { 2, 2, 3, 5, 5 };
 
    int uniqueFactors = factorsOf300.Distinct().Count();
 
    Console.WriteLine("There are {0} unique factors of 300.", uniqueFactors);
}

Result

There are 3 unique factors of 300.

Count - Conditional

This sample uses Count to get the number of odd ints in the array.

public void Linq74()
{
    int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
 
    int oddNumbers = numbers.Count(n => n % 2 == 1);
 
    Console.WriteLine("There are {0} odd numbers in the list.", oddNumbers);
}

Result

There are 5 odd numbers in the list.

Count - Nested

This sample uses Count to return a list of customers and how many orders each has.

public void Linq76()
{
    List<Customer> customers = GetCustomerList();
 
    var orderCounts =
        from c in customers
        select new { c.CustomerID, OrderCount = c.Orders.Count() };
 
    ObjectDumper.Write(orderCounts);
}

Result

CustomerID=ALFKI  CustomerID=ANATR  CustomerID=ANTON  CustomerID=AROUT  CustomerID=BERGS  CustomerID=BLAUS  CustomerID=BLONP  CustomerID=BOLID  CustomerID=BONAP  CustomerID=BOTTM  CustomerID=BSBEV  CustomerID=CACTU  CustomerID=CENTC  CustomerID=CHOPS  CustomerID=COMMI  CustomerID=CONSH  CustomerID=DRACD  CustomerID=DUMON  CustomerID=EASTC  CustomerID=ERNSH  CustomerID=FAMIA  CustomerID=FISSA  CustomerID=FOLIG  CustomerID=FOLKO  CustomerID=FRANK  CustomerID=FRANR  CustomerID=FRANS  CustomerID=FURIB  CustomerID=GALED  CustomerID=GODOS  CustomerID=GOURL  CustomerID=GREAL  CustomerID=GROSR  CustomerID=HANAR  CustomerID=HILAA  CustomerID=HUNGC  CustomerID=HUNGO  CustomerID=ISLAT  CustomerID=KOENE  CustomerID=LACOR  CustomerID=LAMAI  CustomerID=LAUGB  CustomerID=LAZYK  CustomerID=LEHMS  CustomerID=LETSS  CustomerID=LILAS  CustomerID=LINOD  CustomerID=LONEP  CustomerID=MAGAA  CustomerID=MAISD  CustomerID=MEREP  CustomerID=MORGK  CustomerID=NORTS  CustomerID=OCEAN  CustomerID=OLDWO  CustomerID=OTTIK  CustomerID=PARIS  CustomerID=PERIC  CustomerID=PICCO  CustomerID=PRINI  CustomerID=QUEDE  CustomerID=QUEEN  CustomerID=QUICK  CustomerID=RANCH  CustomerID=RATTC  CustomerID=REGGC  CustomerID=RICAR  CustomerID=RICSU  CustomerID=ROMEY  CustomerID=SANTG  CustomerID=SAVEA  CustomerID=SEVES  CustomerID=SIMOB  CustomerID=SPECD  CustomerID=SPLIR  CustomerID=SUPRD  CustomerID=THEBI  CustomerID=THECR  CustomerID=TOMSP  CustomerID=TORTU  CustomerID=TRADH  CustomerID=TRAIH  CustomerID=VAFFE  CustomerID=VICTE  CustomerID=VINET  CustomerID=WANDK  CustomerID=WARTH  CustomerID=WELLI  CustomerID=WHITC  CustomerID=WILMK  CustomerID=WOLZA

OrderCount=6  OrderCount=4  OrderCount=7  OrderCount=13  OrderCount=18  OrderCount=7  OrderCount=11  OrderCount=3  OrderCount=17  OrderCount=14  OrderCount=10  OrderCount=6  OrderCount=1  OrderCount=8  OrderCount=5  OrderCount=3  OrderCount=6  OrderCount=4  OrderCount=8  OrderCount=30  OrderCount=7  OrderCount=0  OrderCount=5  OrderCount=19  OrderCount=15  OrderCount=3  OrderCount=6  OrderCount=8  OrderCount=5  OrderCount=10  OrderCount=9  OrderCount=11  OrderCount=2  OrderCount=14  OrderCount=18  OrderCount=5  OrderCount=19  OrderCount=10  OrderCount=14  OrderCount=4  OrderCount=14  OrderCount=3  OrderCount=2  OrderCount=15  OrderCount=4  OrderCount=14  OrderCount=12  OrderCount=8  OrderCount=10  OrderCount=7  OrderCount=13  OrderCount=5  OrderCount=3  OrderCount=5  OrderCount=10  OrderCount=9  OrderCount=0  OrderCount=6  OrderCount=10  OrderCount=6  OrderCount=9  OrderCount=13  OrderCount=28  OrderCount=5  OrderCount=18  OrderCount=12  OrderCount=11  OrderCount=10  OrderCount=5  OrderCount=6  OrderCount=31  OrderCount=9  OrderCount=7  OrderCount=4  OrderCount=9  OrderCount=12  OrderCount=4  OrderCount=3  OrderCount=5  OrderCount=10  OrderCount=7  OrderCount=3  OrderCount=11  OrderCount=10  OrderCount=4  OrderCount=10  OrderCount=15  OrderCount=9  OrderCount=14  OrderCount=8  OrderCount=7

Count - Grouped

This sample uses Count to return a list of categories and how many products each has.

public void Linq77()
{
    List<Product> products = GetProductList();
 
    var categoryCounts =
        from p in products
        group p by p.Category into g
        select new { Category = g.Key, ProductCount = g.Count() };
 
    ObjectDumper.Write(categoryCounts
}

Result

Category=Beverages  Category=Condiments  Category=Produce  Category=Meat/Poultry  Category=Seafood  Category=Dairy Products  Category=Confections  Category=Grains/Cereals

ProductCount=12  ProductCount=12  ProductCount=5  ProductCount=6  ProductCount=12  ProductCount=10  ProductCount=13  ProductCount=7

Sum - Simple

This sample uses Sum to get the total of the numbers in an array.

public void Linq78()
{
    int[] numbers = {