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C# All Method: All Elements Match a ConditionUse the All extension method from System.Linq to determine if all elements match a condition.
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All. This is an extension method. It tells us if all the elements in a collection match a certain condition. It returns true or false.
System.Linq. All() is part of the System.Linq namespace in .NET. We often want to call All() on the result of a query expression using other LINQ features.
An example. To begin, include the System.Linq namespace. Next, pass in a lambda expression to the All method. We pass 1 argument to the All() method, usually a lambda expression.
Argument This lambda receives 1 parameter (the type of element in the collection), and returns 1 bool (whether it matches the condition).
Extension
Predicate
Bool
Info We invoke All() on the integer array with 3 different lambdas. The All() method returns true, false and then true again.
C# program that uses All method
using System; using System.Linq; class Program { static void Main() { int[] array = { 10, 20, 30 }; // Are all elements >= 10? YES bool a = array.All(element => element >= 10); // Are all elements >= 20? NO bool b = array.All(element => element >= 20); // Are all elements < 40? YES bool c = array.All(element => element < 40); Console.WriteLine(a); Console.WriteLine(b); Console.WriteLine(c); } }
True False True
List, query example. We can use All() on a query expression to create more complex meanings. Here we use All() on a List generic type.
List
Length We select all strings from the List that have lengths of exactly 4 characters.
Where
String Length
All This returns true if all elements in the query result are equal to their uppercase forms (in other words, are uppercase strings).
True The All() method returns true because all 4-letter strings are uppercase strings.
True, False
C# program that uses List, query and All
using System; using System.Linq; using System.Collections.Generic; class Program { static void Main() { var colors = new List<string>() { "BLUE", "GREY", "white" }; // True if all strings of length 4 are in uppercase. var result = (from color in colors where color.Length == 4 select color).All(element => element == element.ToUpper()); Console.WriteLine("RESULT: {0}", result); } }
RESULT: True
Benefits. Why would we use All() instead of looping over elements and using an if-statement? The All method is more compact. And it can be part of a more complex LINQ statement.
Also All() is probably slower due to the requirement that a Func instance be created.
Func
Note Performance is often more important than fancy syntax—this depends on the program.
A summary. As part of the LINQ extensions, All() serves a specific purpose. For arrays, we can also use the Array.TrueForAll method, which uses the same syntax but is a static method.
Array.TrueForAll
Static
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