Linq Cheatsheet

LINQ CHEAT SHEET

Query Syntax

Lambda Syntax

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 col9 = from o in orders

  orderby o.CustomerID, o.Cost descending

           select o;

//returns same results as above

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);

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.LINQ CHEAT SHEET

Query Syntax

Lambda Syntax

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

            select c).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(new Customer()).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();

//returns 0 if no elements

var i = (from c in customers

         where c.CustomerID == 85

         select c.CustomerID).SingleOrDefault();

var j = customers.Where(

        c => c.CustomerID == 85).

        Select(o => o.CustomerID).SingleOrDefault();

NOTE:

Single, Last, First, ElementAt all throw exceptions if source sequence is empty.

SingleOrDefault, LastOrDefault, FirstOrDefault, ElementAtOrDefault all return default(T) if source

sequence is empty.  i.e. NULL will be returned if T is a reference type or nullable value type; default(T) will be returned if T is a

non-nullable value type (int, bool etc). This can be seen in the last example above.LINQ CHEAT SHEET

Query Syntax

Lambda Syntax

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 in orders                                                                    

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);