Filtering, Projecting, and Ordering Data using LINQ Syntax

Mastering the Core Operations That Power LINQ Queries

LINQ (Language Integrated Query) revolutionised how C# developers interact with data.
Instead of juggling loops, lists, and conditionals, you can describe what you want – and let LINQ handle the how.

In this tutorial, we’ll explore three of LINQ’s most essential operations — Filtering, Projecting, and Ordering — and how they work together to turn raw data into structured, meaningful results.

🔹 LINQ Syntax Overview

LINQ brings SQL-style querying directly into C#:

var results = from item in collection
              where item.Price > 50
              orderby item.Name
              select item.Name;

This declarative style is both readable and powerful — and works on arrays, lists, XML, databases, and more.

🔹 Filtering Data – Using where

Filtering is about narrowing your data set down to only what’s relevant.
The where clause acts like a filter condition, just like WHERE in SQL.

Example:

var numbers = new[] { 5, 10, 15, 20, 25, 30 };

var filtered = from n in numbers
               where n > 10 && n < 30
               select n;

Output:

15, 20, 25

✅ Best for:

• Removing unwanted data
• Combining multiple logical expressions (&&, ||, !)
• Filtering based on string, numeric, or object criteria

🔧 Tip:
You can use methods inside where:

where name.StartsWith("A") || name.EndsWith("s")

🔹 Projecting Data – Using select

Projection means transforming your data into a new form — selecting only the parts you need, or creating entirely new objects.

Example 1 – Selecting specific fields

var students = new[]
{
    new { Name = "Alice", Age = 22 },
    new { Name = "Bob", Age = 25 },
    new { Name = "Clara", Age = 20 }
};

var names = from s in students
            select s.Name;

Output:

Alice, Bob, Clara

Example 2 – Creating new anonymous types

var projections = from s in students
                  select new { StudentName = s.Name, NextYearAge = s.Age + 1 };

Output:

StudentName = Alice, NextYearAge = 23
StudentName = Bob, NextYearAge = 26
StudentName = Clara, NextYearAge = 21

✅ Best for:

• Extracting key information
• Reshaping data for output or display
• Building lightweight view models

🔧 Tip:
Use select new { ... } to construct flexible, temporary types for reports and UI binding.

🔹 Ordering Data – Using orderby

Sorting helps you present or process data in a specific sequence.
By default, orderby sorts ascending, but you can easily specify descending.

Example 1 – Simple ascending sort

var fruits = new[] { "Orange", "Apple", "Mango", "Banana" };

var sorted = from f in fruits
             orderby f
             select f;

Output:

Apple, Banana, Mango, Orange

Example 2 – Descending and multi-level sort

var employees = new[]
{
    new { Name = "John", Department = "Sales", Salary = 50000 },
    new { Name = "Anna", Department = "Sales", Salary = 55000 },
    new { Name = "Mark", Department = "IT", Salary = 60000 },
    new { Name = "Lucy", Department = "IT", Salary = 58000 }
};

var sortedEmps =
    from e in employees
    orderby e.Department, e.Salary descending
    select e;

Output:

Department: IT  → Mark (60000), Lucy (58000)
Department: Sales → Anna (55000), John (50000)

✅ Best for:

• Displaying results in user-friendly order
• Sorting by multiple fields
• Combining with filtering for precise control

🔧 Tip:
To reverse the order later, use .Reverse() after the query.

🧩 Combined Example – Filter → Project → Order

Let’s combine everything into one practical LINQ query.

var products = new[]
{
    new { Name = "Laptop", Price = 1200 },
    new { Name = "Mouse", Price = 25 },
    new { Name = "Keyboard", Price = 45 },
    new { Name = "Monitor", Price = 200 }
};

var query =
    from p in products
    where p.Price > 30
    orderby p.Price descending
    select new
    {
        Product = p.Name,
        Discounted = p.Price * 0.9
    };

Output:

Product = Laptop, Discounted = 1080
Product = Monitor, Discounted = 180
Product = Keyboard, Discounted = 40.5

✅ What’s Happening:

• where filters out cheap products
• orderby sorts by price, highest first
• select projects a new result showing a discounted value

📚 Summary

✅ Best Practices

• Keep queries declarative and readable — avoid deeply nested logic
• Filter early using where to reduce data before sorting
• Always specify descending explicitly when needed
• Use select to create lightweight, anonymous result sets
• Chain filters and sorts logically: Filter → Order → Project

🧪 Challenge Task

Write a LINQ query for a list of employees that:

• Filters out anyone earning below £40,000
• Orders the results by department (ascending) and salary (descending)
• Projects a new object with { Name, Department, AnnualBonus = Salary * 0.1 }

Example:

var staff = new[]
{
    new { Name = "Tom", Department = "IT", Salary = 60000 },
    new { Name = "Emma", Department = "HR", Salary = 35000 },
    new { Name = "Sam", Department = "Finance", Salary = 50000 }
};

👨‍💻 Want More?

Our Advanced C# Course dives deeper into:

• Filtering, ordering, grouping, and joining data
• Working with LINQ to Objects and LINQ to SQL
• Real-world scenarios using collections and databases
• Optimizing query performance and clarity

Master these LINQ fundamentals and you’ll write data-handling code that’s clean, fast, and professional.