LINQ First Query Operator

By Peter Bromberg

LINQ First Query Operator returns the first element of a sequence. This member is overloaded. First<TSource>(IEnumerable<TSource>) Returns the first element of a sequence. First<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>) Returns the first element in a sequence that satisfies a specified condition.

// Create a new generic list of ints
   List<int> l = new List<int>();

    l.Add(1); // Add 1 to the list
    l.Add(5); // Add 5 to the list
    l.Add(3); // Add 3 to the list

    // Returns 1 as only 1 satisfies the condition
    int value = l.First(i => i == 1);

    // Returns 5 although both 5 and 3 are greater than 1
    // since 5 appears first in the list
    value = l.First(i => i > 1);

    // Returns the default value of int which is 0
    // since no element in the list equals 4
    value = l.FirstOrDefault(i => i == 4);
    
    // Throws System.InvalidOperationException
    // since no element in the list equals 4
    value = l.First(i => i == 4);

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