C# LINQ Introduction


Filtering data witn LINQ methods

How can we apply LINQ to our example of filtering positive and negative numbers? As stated in the introduction, LINQ is a set of methods which allow you to perform filtering, ordering and grouping operations on collections with a minimum of code.

Let's jump right to a code example. As you allready know about lambda expressions and how to pass them as an argument to a method, writing LINQ method syntax queries is quite self explaining.

Filtering with LINQ

The code explained

Yes, this is it! What should I say?

KeepPositiveNumbers returns all numbers x, where x > 0.
KeepNegativeNumbers returns all numbers x, where x < 0.

This is LINQ!

We have now applied LINQ to filter our data by passing a predicate to the Where method. But there is more then Where. As in .Net 6 there are 63 other LINQ methods you can apply to collections to filter, order, group or transform your data.

We will cover the most common ones in the next sections.

Try it yourself

Now it's time to write some code yourself: Select all numbers, that are equal to 0.

Filtering with LINQ Exercise

Working with objects

For the next examples we will use real objects instead of primitive data types such as int. From now on, we use a Person wiht a Name and Age (years from date of birth until now).

public class Person {
    public string Name { get; set; }
    public int Age { get; set; }
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