!!!C# LINQ使用例
[C#][C# サンプルコード]
*[国立国会図書館API|http://iss.ndl.go.jp/information/api/]
 using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using System.Net;
 using System.Reflection;
 using System.Text;
 using System.Threading.Tasks;
 using System.Xml;
 using System.Xml.Linq;
 
 namespace Book
 {
     class Program
     {
         static void Main(string[] args)
         {
             var p = new Program();
             if (args.Length < 2)
             {
                 Console.WriteLine("must 2 arguments.");
                 return;
             }
             string option = args[0];
 
             string xml = null;
             if (option == "-f")
             {
                 xml = File.ReadAllText(args[1],Encoding.UTF8);
             }
             else if (option == "-k")
             {
                 var param = new List<KeyValuePair<string, string>>();
                 for (int i=1; i<args.Length; i++)
                 {
                     string[] kv = args[i].Split('=');
                     param.Add(new KeyValuePair<string, string>(kv[0], kv?[1]));
                 }
                 xml = p.GetXml(param);
             }
             else if (option == "-t")
             {
                 var param = new List<KeyValuePair<string, string>>();
                 param.Add(new KeyValuePair<string, string>("title", "Python"));
                 xml = p.GetXml(param);
             }
             var books = ParseXml(xml);
 
             LinqTest(books);
         }
 
         private static void LinqTest(List<Book> books)
         {
 
             // QueryExp(books);
             MethodExp(books);
 
         }
 
         /// <summary>
         /// メソッド構文
         /// </summary>
         /// <param name="books"></param>
         private static void MethodExp(List<Book> books)
         {
             var result = books
                         .Where( book => book.Title.IndexOf("計算") > 0 )
                         .OrderByDescending( book=> book.Title)
                         .Select( book => book.Title)
 
              ;
 
             foreach (string title in result)
             {
                 Console.WriteLine(title);
             }
         }
 
         /// <summary>
         /// クエリ構文
         /// </summary>
         /// <param name="books"></param>
         private static void QueryExp(List<Book> books)
         {
             var result = from book in books
                          where book.Title.IndexOf("計算") > 0
                          orderby book.Title descending
                          select book.Title
              ;
 
             // 遅延評価
             // books.ForEach(book => book.Title = book.Title.Replace("Python", "HOGE"));
 
             foreach (string title in result)
             {
                 Console.WriteLine(title);
             }
         }
 
         private static List<Book> ParseXml(string xml)
         {
             XNamespace xmlns = "http://www.loc.gov/zing/srw/";
             XNamespace xmlns2 = "info:srw/schema/1/dc-v1.1";
             XNamespace xmlns3 = "http://purl.org/dc/elements/1.1/";
             
             var root = XElement.Load(new XmlTextReader(new StringReader(xml)));
 
             var records = from record in root.Elements(xmlns + "records")
                                             .Elements(xmlns + "record")
                                             .Elements(xmlns + "recordData")
                                             .Elements(xmlns2 + "dc")
                           select record
                           ;
 
             var books = new List<Book>();
             foreach (XElement record in records)
             {
 
                 var book = new Book();
                 books.Add(book);
 
                 foreach(PropertyInfo field in book.GetType().GetProperties())
                 {
                     foreach (var elms in record.Elements(xmlns3 + field.Name.ToLower()))
                     {
                         field.SetMethod?.Invoke(book, new object[] { elms.Value });
                         break;
                     }
                 }
 
             }
             return books;
         }
 
         class Book
         {
             public string Title { get; set; } = "";
             public string Creator { get; set; } = "";
             public string Subject { get; set; } = "";
             public string Publisher { get; set; } = "";
             public string Language { get; set; } = "";
 
             public override string ToString()
             {
                 var buf = new StringBuilder();
                 buf.Append($"{this.GetType().Name}{{");
                 foreach(PropertyInfo p in  this.GetType().GetProperties())
                 {
                     buf.Append($"{p.Name}={p.GetValue(this)},");
                 }
 
                 buf.Append($"}}");
                 return buf.ToString();
             }
         }
 
         public string GetUrl(List<KeyValuePair<string, string>> param)
         {
             string url = "http://iss.ndl.go.jp/api/sru?operation=searchRetrieve&recordPacking=xml&query={0}";
             string qp = string.Join(" OR ",
                 param.Select(kvp => WebUtility.UrlEncode(String.Format("{0}=\"{1}\"", kvp.Key, kvp.Value))));
             return string.Format(url, qp);
         }
 
         public string GetXml(List<KeyValuePair<string, string>> param)
         {
             string url = GetUrl(param);
             
             using (var client = new WebClient())
             {
                 using (var reader = new StreamReader(client.OpenRead(url)))
                 {
                     string xml = reader.ReadToEnd();
                     Console.WriteLine(xml);
                     return xml;
                 }
             }
         }
     }
 }