玩轉C#之【LINQ 語法介紹】

環境準備

語法說明

Where

List<Student> students = GetStudentList();
var student = students.Where(x=>x.Age > 30);

First

List<Student> students = GetStudentList();
var student = students.First();

List<Student> students = GetStudentList();
var student = students.First(x=>x.Age < 25);

FirstOrDefault

List<Student> students = GetStudentList();
var student = students.FirstOrDefault(x=>x.Age < 1);

Select

List<Student> students = GetStudentList();
var student = students.Where(x=>x.Age >5).Select(x=>x.Name);

List<Student> students = GetStudentList();
var student = students.Where(x => x.Age > 5).Select(x =>new{x.Name,x.Age});

List<Student> students = GetStudentList();
var student = students.Select(x =>new{x.Name,age = x.Age > 25?”老妹”:”正妹”});

public class Girl
{
public string Name { get; set; }
public int Age { get; set; }
}
List<Student> students = GetStudentList();
var student = students.Select(x =>new Girl{Name = x.Name,Age = x.Age});

List<Student> students = GetStudentList();
var student = students.Select(x =>x.Age).Distinct();

Count

List<Student> students = GetStudentList();
var student = students.Count();

List<Student> students = GetStudentList();
var student = students.Count(x=>x.Age>30);

List<Student> students = GetStudentList();
var student = students.LongCount();

public static TSource Aggregate<TSource>(this IEnumerable<TSource> source, Func<TSource, TSource, TSource> func)
 {
 if (source == null)
 {
 throw Error.ArgumentNull(“source”);
 }
 if (func == null)
 {
 throw Error.ArgumentNull(“func”);
 }
 using (IEnumerator<TSource> enumerator = source.GetEnumerator())
 {
 if (!enumerator.MoveNext())
 {
 throw Error.NoElements();
 }
 TSource val = enumerator.Current;
 while (enumerator.MoveNext())
 {
 val = func(val, enumerator.Current);
 }
 return val;
 }
 }

int[] Source = new int[] { 2, 7, 5, 1, 6, 8, 3 };
Source.Aggregate((total, next) => total + next)

public static TAccumulate Aggregate<TSource, TAccumulate>(this IEnumerable<TSource> source, TAccumulate seed, Func<TAccumulate, TSource, TAccumulate> func)
 {
 if (source == null)
 {
 throw Error.ArgumentNull(“source”);
 }
 if (func == null)
 {
 throw Error.ArgumentNull(“func”);
 }
 TAccumulate val = seed;
 foreach (TSource item in source)
 {
 val = func(val, item);
 }
 return val;
 }

int[] Source = new int[] { 2, 7, 5, 1, 6, 8, 3 };
Source.Aggregate(60,(total, next) => total + next);

參考資料