LINQ - sklab @ ウィキ

クエリ式

• 基本

  int[] numbers = {1,2,3,4,5};
  var query = from n in numbers where n >= 2 && n <= 4 select n;
  foreach(var a in query) Console.WriteLine(a);
  

• 文字列から特定の文字を含むデータを取り出す

  string[] str = { "test00", "test01", "test02" }; 
  var query = from s in str where s.Contains("01") select s;
  foreach (var s in query) Console.WriteLine(s); 
  

• select句におけるデータの加工処理

  int[] price = {100,200,300};
  var query = from n in price select n * 1.05;
  

• インスタンスのデータを加工

  class Fruit{
    public string code;
    public string name;
    public int price;
  }
  class Program{
    static void Main(string[] args){
       Fruit[] f = { new Fruit(){ code="A110",name="Apple",price=200},
                     new Fruit(){ code="G201",name="Orange",price=150}
                   };
       var query = from n in f select n;
       foreach(var a in query){
               Console.WriteLine("{0},{1},{2}",a.code,a.name,a.price);
       }
  

• Selectメソッド内部動作

  public static IEnumerable<TResult> Select<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, int, TResult> selector) { 
   if (source == null) throw Error.ArgumentNull("source"); 
   if (selector == null) throw Error.ArgumentNull("selector"); 
   return SelectIterator<TSource, TResult>(source, selector); 
  } 
  static IEnumerable<TResult> SelectIterator<TSource, TResult>(IEnumerable<TSource> source, Func<TSource, int, TResult> selector) { 
   int index = -1; 
   foreach (TSource element in source) { 
    checked { index++; } 
    yield return selector(element, index); 
   } 
  }