在下面的代码中,我们可以显示Select
和SelectMany
运算符之间的差异。
有没有办法避免常用技巧?例如,如果两名员工拥有C#技能,那么我只想打印一次。
namespace LinqOperators
{
class Employee
{
public string Name { get; set; }
public List<string> Skills { get; set; }
}
class Program
{
static void Main(string[] args)
{
List<Employee> employees = new List<Employee>();
Employee emp1 = new Employee { Name = "Deepak", Skills = new List<string> { "C", "C++", "Java" } };//Adding Skills List to Employee List i.e List of List
Employee emp2 = new Employee { Name = "Karan", Skills = new List<string> { "SQL Server", "C#", "ASP.NET" } };
Employee emp3 = new Employee { Name = "Lalit", Skills = new List<string> { "C#", "ASP.NET MVC", "Windows Azure", "SQL Server" } };
employees.Add(emp1);
employees.Add(emp2);
employees.Add(emp3);
// Query using Select()
IEnumerable<List<String>> resultSelect = employees.Select(e => e.Skills);
Console.WriteLine("**************** Select ******************");
// Two foreach loops are required to iterate through the results
// because the query returns a collection of arrays.
foreach (List<String> skillList in resultSelect)
{
foreach (string skill in skillList)
{
Console.WriteLine(skill);
}
Console.WriteLine();//To differntiate Two Skill Lists
}
// Query using SelectMany()
IEnumerable<string> resultSelectMany = employees.SelectMany(emp => emp.Skills);
Console.WriteLine("**************** SelectMany ******************");
// Only one foreach loop is required to iterate through the results
// since query returns a one-dimensional collection.
foreach (string skill in resultSelectMany)
{
Console.WriteLine(skill);
}
Console.ReadKey();
}
}
}
答案 0 :(得分:4)
SelectMany
会压扁您的IEnumerable
,使其不会产生IEnumerable of IEnumerables
但IEnumerable
:
IEnumerable<IEnumerable<string>> skills; //not this [[C#, Java], [C, C++, Java, C#]]
IEnumerable<string> skills; //but this [C#, Java, C, C++, Java, C#]
您可以在Distinct
中使用resultSelectMany
仅获得一次普通技能。
resultSelectMany = resultSelectMany.Distinct(); //[C#, Java, C, C++]
或者把它放在同一行:
// Query using SelectMany()
IEnumerable<string> resultSelectMany = employees.SelectMany(emp => emp.Skills).Distinct();
答案 1 :(得分:1)
您可以使用additional encoders删除重复项