C# LINQ basics: Where, Select and OrderBy

Use Where to keep items that pass a test, Select to change each item into something else, and OrderBy to sort. Chain them as Where, then OrderBy, then Select, and finish with ToList().

Filter, sort and project a menu

List<MenuItem> menu =
[
    new MenuItem("Espresso", 3.25m), new MenuItem("Latte", 4.75m),
    new MenuItem("Cold brew", 4.25m), new MenuItem("Drip coffee", 2.75m),
    new MenuItem("Blueberry muffin", 3.50m),
];

var result = menu.Where(item => item.Price < 4.50m)
                 .OrderBy(item => item.Price)
                 .Select(item => $"{item.Name} ({item.Price:0.00})")
                 .ToList();

foreach (var line in result)
{
    Console.WriteLine(line);
}

record MenuItem(string Name, decimal Price);

Output:

Drip coffee (2.75)
Espresso (3.25)
Blueberry muffin (3.50)
Cold brew (4.25)

How it works

LINQ is a set of methods that work on any list or array. In a normal dotnet project the using System.Linq; line is already added for you.

• item => item.Price < 4.50m is a lambda: a tiny method written in place. The name on the left of => is the parameter (you pick it), and the value on the right is what it returns.
• Where calls the lambda once per item and keeps the ones that give true. The Latte costs 4.75, so it is dropped.
• OrderBy sorts by the value the lambda returns, smallest first. Use OrderByDescending for largest first, and ThenBy to break ties.
• Select turns each item into something new. Here each MenuItem becomes a string.
• ToList() finishes the chain and gives you a real List. Use ToArray() if you want an array.

None of these methods change menu. They build a new result each time.

Common mistake

Putting Select before Where or OrderBy and then asking for a property that no longer exists:

// Error: a string has no Price
var bad = menu.Select(item => item.Name).Where(name => name.Price < 4m);

After Select, you are working with whatever it returned. Filter and sort first, then project:

var good = menu.Where(item => item.Price < 4m).Select(item => item.Name).ToList();

Also remember the final ToList(). Without it you have a sequence, not a list, so .Count and indexing like result[0] will not work.

Takeaway

Read a LINQ chain top to bottom: filter with Where, sort with OrderBy, reshape with Select, then call ToList().