How to Use LINQ All in C# for Condition Checks

Use LINQ All in C# to check if every element in a collection meets a specific condition by passing a predicate function. It returns true if all elements satisfy the condition, otherwise false.

Syntax

The All method is called on a collection and takes a predicate function as a parameter. This function defines the condition to check for each element.

• collection.All(element => condition)
• collection: The list or array to check.
• element: Each item in the collection.
• condition: A boolean expression that must be true for all elements.

csharp

bool result = collection.All(element => element > 0);

Example

This example shows how to use All to check if all numbers in an array are positive.

csharp

using System;
using System.Linq;

class Program
{
    static void Main()
    {
        int[] numbers = { 2, 4, 6, 8 };
        bool allPositive = numbers.All(n => n > 0);
        Console.WriteLine($"Are all numbers positive? {allPositive}");

        int[] mixedNumbers = { 2, -4, 6, 8 };
        bool allPositiveMixed = mixedNumbers.All(n => n > 0);
        Console.WriteLine($"Are all numbers positive in mixed array? {allPositiveMixed}");
    }
}

Output

Are all numbers positive? True
Are all numbers positive in mixed array? False

Common Pitfalls

Common mistakes when using All include:

• Passing a predicate that always returns true or false without checking elements.
• Using All on an empty collection, which returns true by default (because no elements violate the condition).
• Confusing All with Any, which checks if any element meets the condition.

csharp

using System;
using System.Linq;

class Program
{
    static void Main()
    {
        int[] empty = { };
        // This returns true because no elements violate the condition
        bool allPositiveEmpty = empty.All(n => n > 0);
        Console.WriteLine($"All positive in empty array? {allPositiveEmpty}");

        // Wrong: predicate always true
        int[] numbers = { 1, 2, 3 };
        bool wrongCheck = numbers.All(n => true);
        Console.WriteLine($"Wrong check (always true): {wrongCheck}");
    }
}

Output

All positive in empty array? True
Wrong check (always true): True

Quick Reference

LINQ All Method Summary:

• Returns true if all elements satisfy the condition.
• Returns true for empty collections.
• Requires a predicate function.
• Useful for validating all items in a list.

Key Takeaways

Use All to check if every element in a collection meets a condition.

All returns true for empty collections by default.

Pass a clear predicate function that returns a boolean for each element.

Do not confuse All with Any which checks if any element matches.

Common mistake: using a predicate that always returns true or false without logic.