What's your favorite LINQ to Objects operator which is not built-in? [closed]

Answer 1

In and NotIn

C# equivalents of two other well-known SQL constructs

/// 

/// Determines if the source value is contained in the list of possible values.
/// 
/// The type of the objects
/// The source value
/// The list of possible values
/// 
///     true if the source value matches at least one of the possible values; otherwise, false.
/// 
public static bool In(this T value, params T[] values)
{
    if (values == null)
        return false;

    if (values.Contains(value))
        return true;

    return false;
}

/// 

/// Determines if the source value is contained in the list of possible values.
/// 
/// The type of the objects
/// The source value
/// The list of possible values
/// 
///     true if the source value matches at least one of the possible values; otherwise, false.
/// 
public static bool In(this T value, IEnumerable values)
{
    if (values == null)
        return false;

    if (values.Contains(value))
        return true;

    return false;
}

/// 

/// Determines if the source value is not contained in the list of possible values.
/// 
/// The type of the objects
/// The source value
/// The list of possible values
/// 
///     false if the source value matches at least one of the possible values; otherwise, true.
/// 
public static bool NotIn(this T value, params T[] values)
{
    return In(value, values) == false;
}

/// 

/// Determines if the source value is not contained in the list of possible values.
/// 
/// The type of the objects
/// The source value
/// The list of possible values
/// 
///     false if the source value matches at least one of the possible values; otherwise, true.
/// 
public static bool NotIn(this T value, IEnumerable values)
{
    return In(value, values) == false;
}