LINQ 의 쿼리문법과 림다문법 비교문서

Filtering

var col = from o in Orders

where o.CustomerID == 84

select o;

var col2 = Orders.Where(o => o.CustomerID == 84);

Return Anonymous Type

var col = from o in orders

select new

{

OrderID = o.OrderID,

Cost = o.Cost

};

var col2 = orders.Select(o => new

{

OrderID = o.OrderID,

Cost = o.Cost

}

);

Ordering

var col = from o in orders

orderby o.Cost ascending

select o;

var col2 = orders.OrderBy(o => o.Cost);

var col3 = from o in orders

orderby o.Cost descending

select o;

var col4 = orders.OrderByDescending(o => o.Cost);

var col5 = from o in orders

orderby o.Cost descending

orderby o.CustomerID

select o;

NOTE the ordering of the orderby’s

var col6 = orders.OrderBy(o => o.CustomerID).ThenByDescending(o => o.Cost);

//Random Ordering

Random R = new Random();

var col6 = from o in orders

orderby R.Next()

select o;

//Random Ordering

Random R = new Random();

var col8 = orders.OrderBy(o => R.Next());

Joining

var col = from c in customers

join o in orders on

c.CustomerID equals

o.CustomerID

select new

{

c.CustomerID,

c.Name,

o.OrderID,

o.Cost

};

var col2 = customers.Join(orders,

c => c.CustomerID,

o => o.CustomerID,

(c, o) => new

{

c.CustomerID,

c.Name,

o.OrderID,

o.Cost

}

);

Grouping

var OrderCounts = from o in orders

group o by o.CustomerID into g

select new

{

CustomerID = g.Key,

TotalOrders = g.Count()

};

var OrderCounts1 = orders.GroupBy(

o => o.CustomerID).

Select(g => new

{

CustomerID = g.Key,

TotalOrders = g.Count()

});

NOTE:
the grouping’s key is the same type as the grouping value. E.g. in above example grouping key is an int because o.CustomerID is an int.

Paging (using Skip & Take)

//select top 3

var col = (from o in orders

where o.CustomerID == 84

select o).Take(3);

var col2 = orders.Where(

o => o.CustomerID == 84

).Take(3);

//skip first 2 and return the 2 after

var col3 = (from o in orders

where o.CustomerID == 84

orderby o.Cost

select o).Skip(2).Take(2);

var col3 = (from o in orders

where o.CustomerID == 84

orderby o.Cost

select o).Skip(2).Take(2);

Element Operators (Single, Last, First, ElementAt, Defaults)

//throws exception if no elements

var cust = (from c in customers

where c.CustomerID == 84

select c).Single();

var cust1 = customers.Single(

c => c.CustomerID == 84);

//returns null if no elements

var cust = (from c in customers

where c.CustomerID == 84

selectc).SingleOrDefault();

var cust1 = customers.SingleOrDefault(

c => c.CustomerID == 84);

//returns a new customer instance if no elements

var cust = (from c in customers

where c.CustomerID == 85

select c).DefaultIfEmpty(

new Customer()).Single();

var cust1 = customers.Where(

c => c.CustomerID == 85

).DefaultIfEmpty(newCustomer()).Single();

//First, Last and ElementAt used in same way

var cust4 = (from o in orders

where o.CustomerID == 84

orderby o.Cost

select o).Last();

var cust5 = orders.Where(

o => o.CustomerID == 84).

OrderBy(o => o.Cost).Last();

NOTE:
Single, Last, First, ElementAt all throw exceptions if source sequence is empty.
SingleOrDefault, LastOrDefault, FirstOrDefault, ElementAtOrDefault all return NULL if source sequence is empty

Conversions

ToArray

string[] names = (from c in customers

select c.Name).ToArray();

ToDictionary

Dictionary<int, Customer> col = customers.ToDictionary(c => c.CustomerID);

Dictionary<string, double> customerOrdersWithMaxCost = (from oc in

(from o inorders join c in customers on o.CustomerID equals c.CustomerID

select new { c.Name, o.Cost })

group oc by oc.Name into g

select g).ToDictionary(g => g.Key, g => g.Max(oc => oc.Cost));

ToList

List<Order> ordersOver10 = (from o in orders

where o.Cost > 10

orderby o.Cost).ToList();

ToLookup

ILookup<int, string> customerLookup =
customers.ToLookup(c => c.CustomerID, c => c.Name);

LINQ CHEAT SHEET.zip

LINQTests.zip

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LINQ 의 쿼리문법과 림다문법 비교문서

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