LINQ Operators And Lambda Expression - Syntax & Examples

LINQ Operators and Lambda Expressions

LINQ is a cool feature in C# 3.0. Most of the developers are struggling for the syntax and examples. Here I have collected various examples for each operator in LINQ and the equivalent Lambda Expressions.

Where

IEnumerable<Product> x = products.Where(p => p.UnitPrice >= 10);

IEnumerable<Product> x =
from p in products
where p.UnitPrice >= 10
select p;

Select

IEnumerable<string> productNames = products.Select(p => p.Name);
IEnumerable<string> productNames = from p in products select p.Name;

var namesAndPrices =
products.
Where(p => p.UnitPrice >= 10).
Select(p => new { p.Name, p.UnitPrice }).
ToList();
IEnumerable<int> indices =
products.
Select((product, index) => new { product, index }).
Where(x => x.product.UnitPrice >= 10).
Select(x => x.index);

SelectMany

IEnumerable<Order> 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.Customer.Name, 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.Name, 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.Name, o.OrderID };

Take

IEnumerable<Product> MostExpensive10 =products.OrderByDescending(p => p.UnitPrice).Take(10);

Skip

IEnumerable<Product> AllButMostExpensive10 = products.OrderByDescending(p => p.UnitPrice).Skip(10);

TakeWhile SkipWhile

s.TakeWhile(p) s.SkipWhile(p)

Join

var custOrders = customers.
Join(orders, c => c.CustomerID, o => o.CustomerID, (c, o) => new {
    c.Name, o.OrderDate, o.Total
});
var custOrders = from c in customers
join o in orders on c.CustomerID equals o.CustomerID
select new {
    c.Name, o.OrderDate, o.Total
};

GroupJoin

var custTotalOrders = customers.
GroupJoin(orders, c => c.CustomerID, o => o.CustomerID, (c, co) => new {
    c.Name, TotalOrders = co.Sum(o => o.Total)
});
var custTotalOrders = from c in customers
join o in orders on c.CustomerID equals o.CustomerID into co
select new {
    c.Name, TotalOrders = co.Sum(o => o.Total)
};
var custTotalOrders = from c in customers
join o in orders on c.CustomerID equals o.CustomerID
select new {
    c.Name, o.OrderDate, o.Total
};
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.Name, o.OrderDate, o.Total
};
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.Name, o.OrderDate, o.Total
};

Concat

IEnumerable < string > locations = customers.Select(c => c.City).
Concat(customers.Select(c => c.Region)).
Concat(customers.Select(c => c.Country)).
Distinct();
IEnumerable < string > locations = new [] {
    customers.Select(c => c.City),
        customers.Select(c => c.Region),
        customers.Select(c => c.Country),
}.
SelectMany(s => s).
Distinct();

OrderBy / ThenBy

IEnumerable<Product> orderedProducts1 =
products.
OrderBy(p => p.Category).
ThenByDescending(p => p.UnitPrice).
ThenBy(p => p.Name);
IEnumerable<Product> orderedProducts1 =
from p in products
orderby p.Category, p.UnitPrice descending, p.Name
select p;
IEnumerable<Product> orderedProducts2 =
products.
Where(p => p.Category == "Beverages").
OrderBy(p => p.Name, StringComparer.CurrentCultureIgnoreCase);
IEnumerable<string> orderedProductNames =
products.
Where(p => p.Category == "Beverages").
Select(p => p.Name).
OrderBy(x => x);

GroupBy

IEnumerable<IGrouping<string, Product>> productsByCategory =products.GroupBy(p => p.Category);
IEnumerable<IGrouping<string, string>> productNamesByCategory =products.GroupBy(p => p.Category, p => p.Name);

Distinct

IEnumerable<string> productCategories =products.Select(p => p.Category).Distinct();

AsEnumerable

Table<Customer> custTable = GetCustomersTable();
var query = custTable.AsEnumerable().Where(c => IsGoodCustomer(c));

ToArray

string[] customerCountries =customers.Select(c => c.Country).Distinct().ToArray();

ToList

List<Customer> customersWithOrdersIn2005 =customers.
Where(c => c.Orders.Any(o => o.OrderDate.Year == 2005)).
ToList();

ToDictionary

Dictionary<int,Order> orders =customers.
SelectMany(c => c.Orders).
Where(o => o.OrderDate.Year == 2005).
ToDictionary(o => o.OrderID);
Dictionary<string,decimal> categoryMaxPrice =products.
GroupBy(p => p.Category).
ToDictionary(g => g.Key, g => g.Group.Max(p => p.UnitPrice));

ToLookup

Lookup<string,Product> productsByCategory =products.ToLookup(p => p.Category);
IEnumerable<Product> beverages = productsByCategory["Beverage"];

OfType

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

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;

First

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

Single

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

ElementAt

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

Range

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

 

Repeat

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

Empty

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

Any

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

All

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

Count

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

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)
});

Min

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

Max

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

Average

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

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)
});