C# - LINQ Where Examples - CSharp Academy

Where is a LINQ functionality to filter data in a query with given criteria.

Each of below examples is presented in C# with both Lambda and Query expression.

1. Collection of strings – single condition

Query collection to get items which start with “b”.

var colors = new List<string>() { "red", "green", "blue", "black", "white" };

1	var colors = new List<string>() { "red", "green", "blue", "black", "white" };

Lambda expression:

var items = colors.Where(x => x.StartsWith("b"));

1	var items = colors.Where(x => x.StartsWith("b"));

Query expression:

var items = from c in colors
            where c.StartsWith("b")
            select c;

var items = from c in colors

where c.StartsWith("b")

select c;

Print to screen:

foreach (var item in items)
    Console.WriteLine(item);

1 2	foreach (var item in items) Console.WriteLine(item);

Result:

blue
black

1 2	blue black

2. Collection of strings – multiple conditions

Query collection to get items with length more than 3 characters and not start with “w”.

var colors = new List<string>() { "red", "green", "blue", "black", "white" };

1	var colors = new List<string>() { "red", "green", "blue", "black", "white" };

Lambda expression:

var items = colors.Where(x => x.Length > 3 && !x.StartsWith("w"));

1	var items = colors.Where(x => x.Length > 3 && !x.StartsWith("w"));

Query expression:

var items = from c in colors
            where c.Length > 3 && !c.StartsWith("w")
            select c;

var items = from c in colors

where c.Length > 3 && !c.StartsWith("w")

select c;

Result:

green
blue
black

green

blue

black

3. Collection of objects – single condition

Company class for example purposes:

public class Company
{
    public string Name { get; set; }
    public int NumberOfEmployees { get; set; }
}

public class Company

{

public string Name { get; set; }

public int NumberOfEmployees { get; set; }

}

Query collection to get companies with more than 5 employees.

var companies = new List<Company>()
{
    new Company() { Name = "Company 1", NumberOfEmployees = 10 },
    new Company() { Name = "Company 2", NumberOfEmployees = 2 },
    new Company() { Name = "Company 3", NumberOfEmployees = 25 },
    new Company() { Name = "Company 4", NumberOfEmployees = 5 },
    new Company() { Name = "Company 5", NumberOfEmployees = 40 }
};

var companies = new List<Company>()

{

new Company() { Name = "Company 1", NumberOfEmployees = 10 },

new Company() { Name = "Company 2", NumberOfEmployees = 2 },

new Company() { Name = "Company 3", NumberOfEmployees = 25 },

new Company() { Name = "Company 4", NumberOfEmployees = 5 },

new Company() { Name = "Company 5", NumberOfEmployees = 40 }

};

Lambda expression:

var items = companies.Where(x => x.NumberOfEmployees > 5);

1	var items = companies.Where(x => x.NumberOfEmployees > 5);

Query expression:

var items = from c in companies
            where c.NumberOfEmployees > 5
            select c;

var items = from c in companies

where c.NumberOfEmployees > 5

select c;

Result:

Company 1
Company 3
Company 5

Company 1

Company 3

Company 5

4. Collection of objects – null item

Query collection to get not null elements where number of employees is more than 5.

var companies = new List<Company>()
{
    new Company() { Name = "Company 1", NumberOfEmployees = 10 },
    null,
    new Company() { Name = "Company 3", NumberOfEmployees = 25 },
    new Company() { Name = "Company 4", NumberOfEmployees = 5 },
    new Company() { Name = "Company 5", NumberOfEmployees = 40 }
};

var companies = new List<Company>()

{

new Company() { Name = "Company 1", NumberOfEmployees = 10 },

null,

new Company() { Name = "Company 3", NumberOfEmployees = 25 },

new Company() { Name = "Company 4", NumberOfEmployees = 5 },

new Company() { Name = "Company 5", NumberOfEmployees = 40 }

};

One of the list elements is null which creates a risk of NullReferenceException. It can be prevented by additional condition: sth != null.

Lambda expression:

var items = companies.Where(x => x != null && x.NumberOfEmployees > 5);

1	var items = companies.Where(x => x != null && x.NumberOfEmployees > 5);

Query expression:

var items = from c in companies
            where c != null && c.NumberOfEmployees > 5
            select c;

var items = from c in companies

where c != null && c.NumberOfEmployees > 5

select c;

Result:

Company 1
Company 3
Company 5

Company 1

Company 3

Company 5

5. Collection of numbers – multiple where

Query collection to get numbers greater than 5 and smaller than 25 using multiple where statements.

var numbers = new List<int>() { 5, 10, 15, 20, 25 };

1	var numbers = new List<int>() { 5, 10, 15, 20, 25 };

Lambda expression:

var items = numbers.Where(x => x > 5).Where(x => x < 25);

1	var items = numbers.Where(x => x > 5).Where(x => x < 25);

Query expression:

var items = from n in numbers
            where n > 5
            where n < 25
            select n;

var items = from n in numbers

where n > 5

where n < 25

select n;

Result:

10
15
20