LINQ, or Language Integrated Query, is a powerful feature of C# and .NET that allows you to write expressive and concise queries over various data sources, such as arrays, collections, databases, XML, and more. In this article, you will learn how to use some of the common LINQ query operators and expressions to limit or skip results in a LINQ query, depending on your needs and preferences.
One way to limit or skip results in a LINQ query is to use the Take and Skip operators, which are extension methods that accept an integer parameter and return an IEnumerable<T> of the same type as the source. The Take operator returns the specified number of elements from the beginning of the source sequence, while the Skip operator returns the remaining elements after skipping the specified number of elements from the beginning. For example, if you have an array of numbers and you want to get the first three and the last three elements, you can write the following LINQ query:
int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
var firstThree = numbers.Take(3); // { 1, 2, 3 }
var lastThree = numbers.Skip(7); // { 8, 9, 10 }
Another way to limit or skip results in a LINQ query is to use the TakeWhile and SkipWhile operators, which are also extension methods that accept a predicate function and return an IEnumerable<T> of the same type as the source. The TakeWhile operator returns the elements from the beginning of the source sequence as long as the predicate function returns true, while the SkipWhile operator returns the remaining elements after skipping the elements from the beginning of the source sequence as long as the predicate function returns true. For example, if you have an array of numbers and you want to get the elements until the first even number and the elements after the first odd number, you can write the following LINQ query:
int[] numbers = { 1, 3, 5, 6, 7, 8, 9, 10 };
var untilEven = numbers.TakeWhile(n => n % 2 != 0); // { 1, 3, 5 }
var afterOdd = numbers.SkipWhile(n => n % 2 == 0); // { 7, 8, 9, 10 }
Actually I have found the snippet wrong. afterOdd variable shall be {1, 3, 5, 6, 7, 8, 9, 10} with predicate `n % 2 == 0` Only if we change predicate to `n => n % 2 != 0`, it skips Even values and it shall be afterEven equal to {6, 7, 8, 9, 10}
A third way to limit or skip results in a LINQ query is to use the Limit and Offset expressions, which are not operators but keywords that can be used in the query syntax. The Limit expression specifies the maximum number of elements to return from the source sequence, while the Offset expression specifies the number of elements to skip from the beginning of the source sequence. For example, if you have a list of products and you want to get the second page of results with five products per page, you can write the following LINQ query:
List<Product> products = GetProducts();
var secondPage = (from p in products
orderby p.Price descending
select p).Limit(5).Offset(5); // { product6, product7, product8, product9, product10 }
Linq doesn't have such keywords and methods as Limit and Offset. So this text and code are not true totally. If you want to give an example of pagination, you must use the same Skip and Take methods. Of course it is possible that some custom library implemente such methods. But there are no such keywords and no such methods in the standard library.
Using limiting or skipping operators in a LINQ query can be beneficial or detrimental depending on the scenario and data source. Advantages include improved performance and memory usage, as well as the ability to implement pagination or filtering features for users. Additionally, query logic can be simplified by using predefined operators or expressions. On the other hand, some information or context may be lost by excluding results, complexity or overhead may be introduced, and differences or limitations may be encountered when translating or executing the operators or expressions across different data providers or platforms.
Very strange point about Advantages and Disadvantages. Because we do not compare a number of algorithms which meet the same goal but different ways. We compare goals, so it doesn't make any sense. It is better to tell readers about translation linq expression to sql query when we run it against database and that Skip becomes `OFFSET` and Take becomes `LIMIT`.