LINQ Operators and Lambda Expression - Syntax & - Examples

The article contains only syntax and example of Linq and Lamda expression, hope this will quit informative for you and thanks to you to give your valuable time in advance.

public class Customers

{

    public string CustomerID;

    public string ContactName;

    public string Phone;

    public string City;

    public string Country;

}

public class Orders

{

    public int OrderID;

    public string CustomerID;

    public DateTime OrderDate;

}

Where

Type Parameters

TSource

The type of the elements of source.

Parameters

source

Type: System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) to filter.

predicate

Type: System.Func(Of TSource, Boolean)
A function to test each element for a condition.

Return Value

Type: System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) that contains elements from the input sequence that satisfy the condition.

#region Where

List<Customers> Customers = new List<Customers>();

IEnumerable<Customers> x = Customers.Where(p => p.ContactName == "MR. ABCD");

IEnumerable<Customers> x = from p in Customers

                           where p.ContactName == "MR. ABCD"

                           select p;

#endregion

Select

Type Parameters

TSource

The type of the elements of source.

TResult

The type of the value returned by selector.

Parameters

source

Type: System.Collections.Generic.IEnumerable(Of TSource)
A sequence of values to invoke a transform function on.

selector

Type: System.Func(Of TSource, TResult)
A transform function to apply to each element.

Return Value

Type: System.Collections.Generic.IEnumerable(Of TResult)
An IEnumerable(Of T) whose elements are the result of invoking the transform function on each element of source.

#region Select

 List<Customers> Customers = new List<Customers>();

 IEnumerable<string> CustomerNames = Customers.Select(p => p.ContactName);

 IEnumerable<string> CustomerNames = from p in Customers select p.ContactName;

 var namesAndCity =

     Customers.

     Where(p => p.City == "Kolkata").

     Select(p => new { p.ContactName, p.City }).

     ToList();

 IEnumerable<int> indices = Customers.

                            Select((Customer, index) => new { Customer, index }).

                            Where(x => x.Customer.ContactName == "Kolkata").

                            Select(x => x.index);

#endregion

SelectMany

Type Parameters

TSource

The type of the elements of source.

TResult

The type of the elements of the sequence returned by selector.

Parameters

source

Type: System.Collections.Generic.IEnumerable(Of TSource)
A sequence of values to project.

selector

Type: System.Func(Of TSource, IEnumerable(Of TResult))
A transform function to apply to each element.

Return Value

Type: System.Collections.Generic.IEnumerable(Of TResult)
An IEnumerable(Of T) whose elements are the result of invoking the one-to-many transform function on each element of the input sequence.

#region SelectMany

List<Customers> Customers = new List<Customers>();

IEnumerable<Orders> orders = Customers.

                             Where(c => c.Country == "Denmark").

                             SelectMany(c => c.Orders);

var namesAndOrderIDs =  Customers.

                        Where(c => c.Country == "Denmark").

                        SelectMany(c => c.Orders).

                        Where(o => o.OrderDate.Year == 2005).

                        Select(o => new { o.CustomerID, o.OrderID });

var namesAndOrderIDs = Customers.

                        Where(c => c.Country == "Denmark").

                        SelectMany(c => c.Orders, (c, o) => new { c, o }).

                        Where(co => co.o.OrderDate.Year == 2005).

                        Select(co => new { co.c.ContactName, co.o.OrderID });

var namesAndOrderIDs =  from c in Customers

                        where c.Country == "Denmark"

                        from o in c.Orders

                        where o.OrderDate.Year == 2005

                        select new { c.ContactName, o.OrderID };

#endregion

Take

Type Parameters

TSource

The type of the elements of source.

Parameters

source

Type: System.Collections.Generic.IEnumerable(Of TSource)
The sequence to return elements from.

count

Type: System.Int32
The number of elements to return.

Return Value

Type: System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) that contains the specified number of elements from the start of the input sequence.

#region Take

List<Customers> Customers = new List<Customers>();

IEnumerable<Customers> MostExpensive10 = Customers.OrderByDescending(p => p.ContactName).Take(10);

#endregion

Skip

Type Parameters

TSource

The type of the elements of source.

Parameters

source

Type: System.Linq.IQueryable(Of TSource)
An IQueryable(Of T) to return elements from.

count

Type: System.Int32
The number of elements to skip before returning the remaining elements.

Return Value

Type: System.Linq.IQueryable(Of TSource)
An IQueryable(Of T) that contains elements that occur after the specified index in the input sequence.

#region Skip

List<Customers> Customers = new List<Customers>();

IEnumerable<Customers> AllButMostExpensive10 = Customers.OrderByDescending(p => p.ContactName).Skip(10);

#endregion

SkipWhile TakeWhile

Type Parameters

TSource

The type of the elements of source.

Parameters

source

Type: System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) to return elements from.

predicate

Type: System.Func(Of TSource, Boolean)
A function to test each element for a condition.

Return Value

Type: System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) that contains the elements from the input sequence starting at the first element in the linear series that does not pass the test specified by predicate.

#region SkipWhile TakeWhile

List<Customers> Customers = new List<Customers>();

var query9 = Customers.Select((cust, index) => new { cust, index })

             .OrderBy(c => c.cust.Country)

             .SkipWhile(c => c.cust.Country != "USA")

             .TakeWhile(c => c.cust.Country == "USA")

             .Select(c => new { c.cust.CustomerID, c.cust.ContactName, c.index });

#endregion

Join

#region Join

List<Customers> Customers = new List<Customers>();

List<Orders> Orders = new List<Orders>();

var custOrders = Customers.

                 Join(Orders, c => c.CustomerID, o => o.CustomerID,

                    (c, o) => new { c.CustomerID, o.OrderDate, o.OrderID });

var custOrders = from c in Customers

                 join o in Orders on c.CustomerID equals o.CustomerID

                 select new { c.ContactName, o.OrderDate, o.OrderID };

#endregion

GroupJoin

Type Parameters

TOuter

The type of the elements of the first sequence.

TInner

The type of the elements of the second sequence.

TKey

The type of the keys returned by the key selector functions.

TResult

The type of the result elements.

Parameters

outer

Type: System.Collections.Generic.IEnumerable(Of TOuter)
The first sequence to join.

inner

Type: System.Collections.Generic.IEnumerable(Of TInner)
The sequence to join to the first sequence.

outerKeySelector

Type: System.Func(Of TOuter, TKey)
A function to extract the join key from each element of the first sequence.

innerKeySelector

Type: System.Func(Of TInner, TKey)
A function to extract the join key from each element of the second sequence.

resultSelector

Type: System.Func(Of TOuter, IEnumerable(Of TInner), TResult)
A function to create a result element from an element from the first sequence and a collection of matching elements from the second sequence.

Return Value

Type: System.Collections.Generic.IEnumerable(Of TResult)
An IEnumerable(Of T) that contains elements of type TResult that are obtained by performing a grouped join on two sequences.

#region GroupJoin

List<Customers> Customers = new List<Customers>();

List<Orders> Orders = new List<Orders>();

Orders emptyOrder = new Orders();

var custTotalOrders = Customers.

                      GroupJoin(Orders, c => c.CustomerID, o => o.CustomerID,

                      (c, co) => new { c.ContactName, TotalOrders = co.Sum(o => o.OrderID) });

var custTotalOrders = from c in Customers

                      join o in Orders on c.CustomerID equals o.CustomerID into co

                      select new { c.ContactName, TotalOrders = co.Sum(o => o.OrderID) };

var custTotalOrders = from c in Customers

                      join o in Orders on c.CustomerID equals o.CustomerID

                      select new { c.ContactName, o.OrderDate, o.OrderID };

var custTotalOrders = from c in Customers

                      join o in Orders on c.CustomerID equals o.CustomerID into co

                      from o in co

                      select new { c.ContactName, o.OrderDate, o.OrderID };

var custTotalOrders = from c in Customers

                      join o in Orders on c.CustomerID equals o.CustomerID into co

                      from o in co.DefaultIfEmpty(emptyOrder)

                      select new { c.ContactName, o.OrderDate, o.OrderDate };

#endregion

Concat

Type Parameters

TSource

The type of the elements of the input sequences.

Parameters

first

Type: System.Collections.Generic.IEnumerable(Of TSource)
The first sequence to concatenate.

second

Type: System.Collections.Generic.IEnumerable(Of TSource)
The sequence to concatenate to the first sequence.

Return Value

Type: System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) that contains the concatenated elements of the two input sequences.

#region Concat

List<Customers> Customers = new List<Customers>();

IEnumerable<string> locations = Customers.Select(c => c.City).

        Concat(Customers.Select(c => c.City)).

        Concat(Customers.Select(c => c.Country)).

        Distinct();

 IEnumerable<string> locations =  new[] {

            Customers.Select(c => c.ContactName),

            Customers.Select(c => c.City),

            Customers.Select(c => c.Country),

        }.SelectMany(s => s)

        .Distinct();

#endregion

OrderBy / ThenBy

Type Parameters

TSource

The type of the elements of source.

TKey

The type of the key returned by keySelector.

Parameters

source

Type: System.Collections.Generic.IEnumerable(Of TSource)
A sequence of values to order.

keySelector

Type: System.Func(Of TSource, TKey)
A function to extract a key from an element.

Return Value

Type: System.Linq.IOrderedEnumerable(Of TSource)
An IOrderedEnumerable(Of TElement) whose elements are sorted according to a key.

#region OrderBy / ThenBy

List<Customers> Customers = new List<Customers>();

List<Orders> Orders = new List<Orders>();

Orders emptyOrder = new Orders();

IEnumerable<Customers> orderedCustomers1 =

            Customers.

            OrderBy(p => p.Country).

            ThenByDescending(p => p.ContactName).

            ThenBy(p => p.Phone);

IEnumerable<Customers> orderedCustomers2 =

                        from p in Customers

                        orderby p.Country, p.ContactName descending, p.Phone

                        select p;

IEnumerable<Customers> orderedCustomers3 =

                        Customers.

                        Where(p => p.Country == "India").

                        OrderBy(p => p.ContactName, StringComparer.CurrentCultureIgnoreCase);

IEnumerable<string> orderedProductNames =

                        Customers.

                        Where(p => p.Country == "India").

                        Select(p => p.ContactName).

                        OrderBy(x => x);

#endregion

GroupBy

Type Parameters

TSource

The type of the elements of source.

TKey

The type of the key returned by keySelector.

Parameters

source

Type: System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) whose elements to group.

keySelector

Type: System.Func(Of TSource, TKey)
A function to extract the key for each element.

Return Value

Type: System.Collections.Generic.IEnumerable(Of IGrouping(Of TKey, TSource))
An IEnumerable<IGrouping<TKey, TSource>> in C# or IEnumerable(Of IGrouping(Of TKey, TSource)) in Visual Basic where each IGrouping(Of TKey, TElement) object contains a sequence of objects and a key.

#region GroupBy

List<Customers> Customers = new List<Customers>();

List<Orders> Orders = new List<Orders>();

Orders emptyOrder = new Orders();

IEnumerable<IGrouping<string, Customers>> CustomersBy = Customers.GroupBy(p => p.Country);

IEnumerable<IGrouping<string, string>> CustomersNamesBy = Customers.GroupBy(p => p.ContactName, p => p.ContactName);

#endregion

#region Distinct

List<Customers> Customers = new List<Customers>();

List<Orders> Orders = new List<Orders>();

Orders emptyOrder = new Orders();

IEnumerable<string> cust = Customers.Select(p => p.ContactName).Distinct();

#endregion

AsEnumerable

#region AsEnumerable

Table<Customers> custTable = GetCustomersTable();

var query = custTable.AsEnumerable().Where(c => IsGoodCustomer(c));

DataTable dt = new DataTable();

var query = dt.AsEnumerable().Where(c => c.Field<String>("Name")=="Your Name");

#endregion

ToArray

Type Parameters

TSource

The type of the elements of source.

Parameters

source

Type: System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) to create an array from.

Return Value

Type: TSource()
An array that contains the elements from the input sequence.

#region ToArray

List<Customers> Customers = new List<Customers>();

string[] customer = Customers.Select(c => c.Country).Distinct().ToArray();

#endregion

ToList

Type Parameters

TSource

The type of the elements of source.

Parameters

source

Type: System.Collections.Generic.IEnumerable(Of TSource)
The IEnumerable(Of T) to create a List(Of T) from.

Return Value

Type: System.Collections.Generic.List(Of TSource)
A List(Of T) that contains elements from the input sequence.

#region ToList

List<Customers> Customers = new List<Customers>();

List<Customers> customers = Customers.

                            Where(c => c.Orders.Any(o => o.OrderDate.Year == 2005)).

                            ToList();

           

#endregion

ToDictionary

Type Parameters

TSource

The type of the elements of source.

TKey

The type of the key returned by keySelector.

Parameters

source

Type: System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) to create a Dictionary(Of TKey, TValue) from.

keySelector

Type: System.Func(Of TSource, TKey)
A function to extract a key from each element.

Return Value

Type: System.Collections.Generic.Dictionary(Of TKey, TSource)
A Dictionary(Of TKey, TValue) that contains keys and values.

#region ToDictionary

List<Customers> Customers = new List<Customers>();

Dictionary<int, Orders> orders = Customers.

                                SelectMany(c => c.Orders).

                                Where(o => o.OrderDate.Year == 2005).

                                ToDictionary(o => o.OrderID);

Dictionary<string, decimal> categoryMaxPrice = Customers.

                                               GroupBy(p => p.Category).

                                               ToDictionary(g => g.Key, g => g.Group.Max(p => p.UnitPrice));

#endregion

Lookup

Type Parameters

TKey

The type of the keys in the Lookup(Of TKey, TElement).

TElement

The type of the elements of each IEnumerable(Of T) value in the Lookup(Of TKey, TElement).

#region Lookup

List<Customers> Customers = new List<Customers>();

Lookup<string, Customers> Country = Customers.ToLookup(p => p.Country);

IEnumerable<Customers> ind = productsByCategory["india"];

#endregion

OfType

#region OfType

List<Person> persons = GetListOfPersons();
IEnumerable<Employee> employees = persons.OfType<Employee>();
#endregion

Cast

Type Parameters

TResult

The type to cast the elements of source to.

Parameters

source

Type: System.Collections.IEnumerable
The IEnumerable that contains the elements to be cast to type TResult.

Return Value

Type: System.Collections.Generic.IEnumerable(Of TResult)
An IEnumerable(Of T) that contains each element of the source sequence cast to the specified type.

#region Cast
ArrayList objects = GetOrders();
IEnumerable<Order> ordersIn2005 =   objects.Cast<Order>().Where(o => o.OrderDate.Year == 2005);

ArrayList objects = GetOrders();
IEnumerable<Order> ordersIn2005 = from Order o in objects where o.OrderDate.Year == 2005 select o;

#endregion

First

Type Parameters

TSource

The type of the elements of source.

Parameters

source

Type: System.Linq.IQueryable(Of TSource)
The IQueryable(Of T) to return the first element of.

Return Value

Type: TSource
The first element in source.

#region First
string phone = "206-555-1212";
Customer c = customers.First(c => c.Phone == phone);
#endregion

Single

Type Parameters

TSource

The type of the elements of source.

Parameters

source

Type: System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) to return the single element of.

Return Value

Type: TSource
The single element of the input sequence.

#region Single
int id = 12345;
Customer c = customers.Single(c => c.CustomerID == id);
#endregion

ElementAt

Type Parameters

TSource

The type of the elements of source.

Parameters

source

Type: System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) to return an element from.

index

Type: System.Int32
The zero-based index of the element to retrieve.

Return Value

Type: TSource
The element at the specified position in the source sequence.

#region ElementAt
Product thirdMostExpensive = products.OrderByDescending(p => p.UnitPrice).ElementAt(2);
#endregion

Range

Parameters

start

Type: System.Int32
The value of the first integer in the sequence.

count

Type: System.Int32
The number of sequential integers to generate.

Return Value

Type: System.Collections.Generic.IEnumerable(Of Int32)
An IEnumerable<Int32> in C# or IEnumerable(Of Int32) in Visual Basic that contains a range of sequential integral numbers.

#region Range
int[] squares = Enumerable.Range(0, 100).Select(x => x * x).ToArray();

#endregion

Repeat

Type Parameters

TResult

The type of the value to be repeated in the result sequence.

Parameters

element

Type: TResult
The value to be repeated.

count

Type: System.Int32
The number of times to repeat the value in the generated sequence.

Return Value

Type: System.Collections.Generic.IEnumerable(Of TResult)
An IEnumerable(Of T) that contains a repeated value.

#region Repeat
long[] x = Enumerable.Repeat(-1L, 256).ToArray();

#endregion

Empty

#region Empty
IEnumerable<Customer> noCustomers = Enumerable.Empty<Customer>();
#endregion

Any

Type Parameters

TSource

The type of the elements of source.

Parameters

source

Type: System.Collections.Generic.IEnumerable(Of TSource)
The IEnumerable(Of T) to check for emptiness.

Return Value

Type: System.Boolean
true if the source sequence contains any elements; otherwise, false.

#region Any
bool b = products.Any(p => p.UnitPrice >= 100 && p.UnitsInStock == 0);
#endregion

All

Type Parameters

TSource

The type of the elements of source.

Parameters

source

Type: System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) that contains the elements to apply the predicate to.

predicate

Type: System.Func(Of TSource, Boolean)
A function to test each element for a condition.

Return Value

Type: System.Boolean
true if every element of the source sequence passes the test in the specified predicate, or if the sequence is empty; otherwise, false.

#region All
IEnumerable<string> fullyStockedCategories =
    products.
    GroupBy(p => p.Category).
    Where(g => g.Group.All(p => p.UnitsInStock > 0)).
    Select(g => g.Key);
#endregion

Count

Type Parameters

TSource

The type of the elements of source.

Parameters

source

Type: System.Collections.Generic.IEnumerable(Of TSource)
A sequence that contains elements to be tested and counted.

predicate

Type: System.Func(Of TSource, Boolean)
A function to test each element for a condition.

Return Value

Type: System.Int32
A number that represents how many elements in the sequence satisfy the condition in the predicate function.

#region Count
int count = customers.Count(c => c.City == "London");
#endregion

Sum

#region Sum
int year = 2005;
var namesAndTotals =
    customers.
    Select(c => new {
        c.Name,
        TotalOrders =
            c.Orders.
            Where(o => o.OrderDate.Year == year).
            Sum(o => o.Total)
    });
#endregion

Min

#region Min
var minPriceByCategory =
    products.
    GroupBy(p => p.Category).
    Select(g => new {
        Category = g.Key,
        MinPrice = g.Group.Min(p => p.UnitPrice)
    });
#endregion

Max

#region Max
decimal largestOrder =
    customers.
    SelectMany(c => c.Orders).
    Where(o => o.OrderDate.Year == 2005).
    Max(o => o.Total);
#endregion

Average

#region Average
var averageOrderTotals =
    customers.
    Select(c => new {
        c.Name,
        AverageOrderTotal = c.Orders.Average(o => o.Total)
    });
#endregion

Aggregate

#region Aggregate
var longestNamesByCategory =
    products.
    GroupBy(p => p.Category).
    Select(g => new {
        Category = g.Key,
        LongestName =
            g.Group.
            Select(p => p.Name).
            Aggregate((s, t) => t.Length > s.Length ? t : s)
    });

#endregion

Posted By: Mr. Palash Paul