bool descending foreach LINQ List orderby Sort true, false

Bool sort

Bools can be sorted. When stored in a C# array or List, they can be ordered with Sort methods. This allows you to order your collection by true or false.

This is useful for promoting or demoting elements programmatically. A sorted list of bools helps us prioritize "true" results over "false" results.

First example

One use for sorting bools is reordering a List of objects. Sometimes, you need to mark some elements in the List as "low priority," pushing them to the bottom of the List.

Part 1 The example populates a List generic with 5 bool values. It displays the List in that state, and then sorts it with List.Sort method.

Part 2 The default Sort method orders the bools from False to True. This is just like ordering 0 to 1.

Part 3 The descending keyword in the example uses the LINQ query syntax, which is useful for sorting.

using System;
using System.Collections.Generic;
using System.Linq;

// Part 1: populate a List of bools.
var items = new List<bool>();
items.Add(true);
items.Add(false);
items.Add(false);
items.Add(false);
items.Add(true);
foreach (bool value in items)
{
    Console.WriteLine("UNSORTED: {0}", value);
}

// Part 2: sort the list.
items.Sort();
foreach (bool value in items)
{
    Console.WriteLine("SORTED: {0}", value);
}

// Part 3: sort descending.
var sorted = from item in items
             orderby item descending
             select item;
foreach (bool value in sorted)
{
    Console.WriteLine("REVERSE SORTED: {0}", value);
}UNSORTED: True
UNSORTED: False
UNSORTED: False
UNSORTED: False
UNSORTED: True
SORTED: False
SORTED: False
SORTED: False
SORTED: True
SORTED: True
REVERSE SORTED: True
REVERSE SORTED: True
REVERSE SORTED: False
REVERSE SORTED: False
REVERSE SORTED: False

Example, `bool` property

Bool sorting can implement a selection algorithm. Only one element should be chosen, but no elements should be eliminated.

Here We create a List of TestData items. We then sort them with the IsImportant property—important items come before unimportant ones.

Info This approach can improve error handling as it does not eliminate any elements from consideration.

Finally We can exit the foreach-loop with a break or return when we find an item that matches our conditions.

using System;
using System.Collections.Generic;
using System.Linq;

class TestData
{
    public bool IsImportant { get; set; }
    public string Data { get; set; }
}

class Program
{
    static void Main()
    {
        // Add data to the list.
        var items = new List<TestData>();
        items.Add(new TestData() { IsImportant = true, Data = "Bird" });
        items.Add(new TestData() { IsImportant = false, Data = "Cat" });
        items.Add(new TestData() { IsImportant = true, Data = "Human" });

        // Sort by bool on class.
        var sorted = from item in items
                     orderby item.IsImportant descending
                     select item;

        // Put "important" items first.
        foreach (var item in sorted)
        {
            Console.WriteLine("ITEM: " + item.IsImportant + "; " + item.Data);
        }
    }
}ITEM: True; Bird
ITEM: True; Human
ITEM: False; Cat

Discussion

To filter, you can add a bool property or field to your class, and then as sign that to true or false depending on whether you want to give the item priority.

So Use true to promote the class. Sort the objects with the LINQ query syntax, using the order by descending clause.

Bools are sorted from false to true. The descending sort will order them from true to false. True is essentially equal to 1, and false to 0.

Use boolean sorting for selection algorithms where some objects should be demoted. This helps when we do not want to eliminate items from consideration, but want to prioritize others.

Bool sort

First example

Example, bool property

Discussion

Example, `bool` property