C# OrderBy, OrderByDescending Examples

Use OrderBy and OrderByDescending from System.Linq. Specify the value to be sorted with a lambda.

OrderByDescending. This sorts elements from high to low. It is an extension method found in the System.Linq namespace. It receives a key selector Func instance.Func Extension

Notes, usage. We pass OrderByDescending a lambda expression that selects the key. The OrderBy method actually means OrderByAscending, as it sorts from low to high.LINQ

OrderByDescending example. Here, each Tuple has 2 items of type int. Next, we call OrderByDescending and use a lambda expression that selects the Item1 property of each Tuple instance.Tuple Lambda

Finally: We see that the Tuples are sorted from the highest Item1 value to the lowest Item1 value.

Info: A reverse sort (a descending sort) is performed. Using descending sorts is usually faster than using a separate reverse pass.

C# program that uses OrderByDescending using System; using System.Linq; class Program { static void Main() { // Create array of tuples. Tuple<int, int>[] tuples = new Tuple<int, int>[3]; tuples[0] = new Tuple<int, int>(3, 6); tuples[1] = new Tuple<int, int>(6, 4); tuples[2] = new Tuple<int, int>(0, 60); // Order by descending on Item1. var result = tuples.OrderByDescending(a => a.Item1); foreach (var item in result) { Console.WriteLine(item); } } } Output (6, 4) (3, 6) (0, 60)

OrderBy example. OrderBy specifies how a collection should be ordered. It is an extension method. We can invoke OrderBy on any collection that implements IEnumerable.IEnumerable

Lambda: This matches the signature of Func as the argument. On the right side of the lambda, we reverse each string to get the sort key.

Array String Literal

Info: We convert to an array with ToCharArray, Reverse the chars, convert to an array with ToArray, and create a string from that array.

ToCharArray Reverse ToArray String Constructor

Finally: The result (of type IOrderedEnumerable) consists of the 4 strings sorted by their characters considered in reverse order.

C# program that uses OrderBy extension method using System; using System.Linq; class Program { static void Main() { // Input array. string[] array = { "the", "glass", "bead", "game" }; // Order alphabetically by reversed strings. var result = array.OrderBy(a => new string(a.ToCharArray().Reverse().ToArray())); // Display results. foreach (var item in result) { Console.WriteLine(item); } } } Output bead the game glass

A discussion. OrderBy and OrderByDescending are often used by the C# compiler when it translates query expressions with the descending contextual keyword.Descending

Tip: Because query expressions do not require explicit delegate syntax (such as lambda expressions =>) they can be easier to read.

Research. I checked the C# specification for details about the descending keyword. When we use "descending," a call of OrderByDescending is added to the translated, method-call syntax.

Quote: If an ordering clause specifies a descending direction indicator, an invocation of OrderByDescending or ThenByDescending is produced instead (The C# Programming Language).

A summary. These 2 methods are sometimes useful. But most often they are used in the translation of query expressions with the orderby and descending keywords.Keywords

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C# OrderBy, OrderByDescending Examples

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