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FirstOrDefault Method

System.Linq

Returns the first element of a sequence, or a default value if the sequence contains no elements.

public static TSource FirstOrDefault<TSource>(this IEnumerable<TSource> source);
public static TSource FirstOrDefault<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate);

Parameters

Return Value

TSource: The first element in the specified sequence that passes the test in the specified predicate, or default (null for reference types, zero for numeric types, false for bool, etc.) if no element passes the test.

Remarks

The FirstOrDefault method returns the first element of a sequence. If the sequence is empty, it returns the default value for the type TSource. If a predicate is provided, it returns the first element that satisfies the predicate, or the default value if no element satisfies the predicate.

The default value for reference types is null, for numeric types it is 0, and for boolean types it is false.

This method has no effect on the current instance and does not return a modified sequence.

The behavior of FirstOrDefault is different from First. First throws an exception if the sequence is empty or no element satisfies the predicate, whereas FirstOrDefault returns the default value.

Examples

Example 1: Basic Usage

Retrieving the first element of a sequence or a default value if the sequence is empty.


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

public class Example
{
    public static void Main(string[] args)
    {
        List<int> numbers1 = new List<int> { 5, 10, 15, 20 };
        int firstOrDefaultNumber1 = numbers1.FirstOrDefault();
        Console.WriteLine($"First or default element: {firstOrDefaultNumber1}"); // Output: 5

        List<int> numbers2 = new List<int>();
        int firstOrDefaultNumber2 = numbers2.FirstOrDefault();
        Console.WriteLine($"First or default element (empty list): {firstOrDefaultNumber2}"); // Output: 0

        List<string> names1 = new List<string> { "Alice", "Bob", "Charlie" };
        string firstOrDefaultName1 = names1.FirstOrDefault();
        Console.WriteLine($"First or default element: {firstOrDefaultName1 ?? "null"}"); // Output: Alice

        List<string> names2 = new List<string>();
        string firstOrDefaultName2 = names2.FirstOrDefault();
        Console.WriteLine($"First or default element (empty list): {firstOrDefaultName2 ?? "null"}"); // Output: null
    }
}

Example 2: With Predicate

Retrieving the first element that satisfies a condition, or a default value if no such element exists.


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

public class Example
{
    public static void Main(string[] args)
    {
        List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6 };

        // Find the first number greater than 3
        int firstGreaterThan3 = numbers.FirstOrDefault(n => n > 3);
        Console.WriteLine($"First number greater than 3: {firstGreaterThan3}"); // Output: 4

        // Find the first number greater than 10 (none exist)
        int firstGreaterThan10 = numbers.FirstOrDefault(n => n > 10);
        Console.WriteLine($"First number greater than 10: {firstGreaterThan10}"); // Output: 0

        List<string> words = new List<string> { "apple", "banana", "cherry" };

        // Find the first word starting with 'b'
        string firstStartingWithB = words.FirstOrDefault(w => w.StartsWith("b"));
        Console.WriteLine($"First word starting with 'b': {firstStartingWithB ?? "null"}"); // Output: banana

        // Find the first word starting with 'z' (none exist)
        string firstStartingWithZ = words.FirstOrDefault(w => w.StartsWith("z"));
        Console.WriteLine($"First word starting with 'z': {firstStartingWithZ ?? "null"}"); // Output: null
    }
}

See Also