descending Extension Func IEnumerable Lambda orderby Tuple

`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.

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

`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.

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.

using System;
using System.Linq;

// 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);
}(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.

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

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

using System;
using System.Linq;

// 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);
}bead
the
game
glass

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

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

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.

OrderByDescending