LINQ - The Take and Skip methods

The partitioning LINQ methods are used to fetch or skip elements from the beginning of an enumerable list while a condition yields true. The Take and Skip methods, and TakeWhile and SkipWhile methods, are complements of one another, meaning that if we concatenate the results from any of these two functional complements we will end up with the same sequence that we started with. These methods are available from .NET Framework 3.5 and onwards.

These are the variations of the four methods that we will be looking at in this article.

• Take<T>
• The Take<T> Method with a Nested Query
• TakeWhile<T>
• TakeWhile<T> Indexed
• Skip<T>
• Skip<T> Nested
• SkipWhile<T>
• SkipWhile<T> Indexed

The Take<T> Method

The Take method is used to fetch items from the beginning of an enumerable sequence for as long as the limiting condition is true. The return value is an IEnumerable<T> containing the items satisfying the...

LINQ Join

Sometimes you need to combine values from two data sequences that don’t have a direct relationship connecting them, using LINQ; this is where the join clause comes to the rescue. To be able to connect the two sources it has to be possible to compare equality on a shared value in both sources. For example, a video store clerk wants to match his list of arrived films with a list if film studio that has released films. A join clause could connect these two lists on the film studio id.

When a join clause compares the equality of a single property or a property of an object in the two sources it uses the special equals keyword. All joins made with the join keyword in LINQ are equijoins, which means that equality is used for comparison of the values.

LINQ joins are optimized for equijoins, but you can perform non-equijoins by using multiple from clauses and use a where clause to apply the predicate expression. The predicate expression could call the Contains method on the...

Foreach

Foreach is used to iterate over a collection or an array of objects or values; it can be anything from a simple list of values to a rows in a dataset table.

When using a foreach loop, you don’t have to know the number of elements that the loop will iterate over because it will iterate over all elements in an array or a collection, unless you explicitly end the loop prematurely.

The following code will loop over the animals in the array.

string[] animals = { "cat", "dog", "bird" };

foreach (string animal in animals)

{

    // Code to execute

}

For

A for loop is a way to iterate over a set of values until the given expression evaluates to false. A for loop has three parts: a start value for the loop, an expression telling the loop when to stop, and a counter.

[int i = 0] is the start value, [i < 100] is the condition that makes the loop iterate 100 times, [i++] is the iterator.

for (int i = 0; i < 100; i++)

{

    // Code to execute a...

Language-Integrated Query (LINQ) is a query language that can be used to query a number of data sources. LINQ is built into .NET Languages such as Visual C# and has standardized, declarative query syntax. You can use LINQ to query data sources such as Collections, ADO.NET dataset, SQL Server databases and XML documents; that is any data source that implements the IEnumerable interface.

Using your knowledge of C# and a few keywords and concepts you don’t have to learn an extra language such as SQL or XQuery to query data sources, you can use the following basic syntax in your C# code when querying data sources with LINQ:

from <variable names> in <data source>

group <grouping criteria>

where <selection criteria>

orderby <result ordering criteria>

select <variable name>

Apart from having a standardized syntax for querying data sources LINQ has many other benefits that need to be mentioned. A huge help when writing the code is compile-time...