ArrayList类型是很早的数据类型,它虽然是一个集合,但里面的元素是object类型的,虽然我们知道,我们这个集合里只存int元素,但因为它自身只实现了IEnumerable接口,而没有实现泛型的版本(它自己在没有泛型之前就有了),因此from-in在书写的时候就会失败。所以,上面的代码是不合理的。 你想想,你转换为foreach后,代码是不是这样: for
var peoples1 = groups1.GroupBy(x => x.Name).Select(item=> new { Name = item.Key,num = item.Sum(x=>x.Number)});//public static IEnumerable<IGrouping<TKey, TSource>> GroupBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector); foreach(var people ...
//聚合操作//最大值varmaxi =(fromiingamesorderbyi ascendingselecti).Max();//最小值varmini = (fromiingamesorderbyi ascendingselecti).Min();//平均值varavar = (fromiinnumbersorderbyi ascendingselecti).Average();//总和varsum = (fromiinnumbersorderbyi ascendingselecti).Sum(); list.Sum(...
Entity Framework:Entity Framework是一种ORM(Object-Relational Mapping)工具,可以将数据库中的表映射为.NET对象,并且支持使用LINQ查询来操作数据库。 LINQ to SQL:类似于Entity Framework,用于在数据库中执行LINQ查询。 LINQ to Objects:这是针对.NET中的对象集合的标准LINQ提供程序,适用于各种集合类型。 LINQ to Ent...
// Return the FileInfo object for the largest file // by sorting and selecting from beginning of list FileInfo longestFile = (from file in fileList let fileInfo = new FileInfo(file) where fileInfo.Length > 0 orderby fileInfo.Length descending select fileInfo ).First(); Consol...
/* 遍历 输出 */foreach(UserSalaryuserinUserSalaryList){Console.WriteLine(PrintUserSalaryObject(user));}/* 输出结果 */{id=1,name=ZhangLong,age=38,gender=True,occupation=Teacher,active=True,salary=7800}{id=2,name=ZhangJin,age=18,gender=False,occupation=Student,active=True,salary=1500}{id=3...
there are "&"different standard functions. Because the object world has no notion of query, a "&"query can only be represented as a string without compile-time type checking or "&"IntelliSense support in the IDE. Transferring data from SQL tables or XML...
// Return the FileInfo object for the largest file// by sorting and selecting from beginning of listFileInfo longestFile = (fromfileinfileListletfileInfo =newFileInfo(file)wherefileInfo.Length >0orderbyfileInfo.LengthdescendingselectfileInfo ).First(); Console.WriteLine($"The larges...
// Return the FileInfo object for the largest file// by sorting and selecting from beginning of listFileInfo longestFile = (fromfileinfileListletfileInfo =newFileInfo(file)wherefileInfo.Length >0orderbyfileInfo.LengthdescendingselectfileInfo ).First(); Console.WriteLine($"The larg...
// Create a new Clump<T> object. Clump<string> fruitClump = new Clump<string> { "apple", "passionfruit", "banana", "mango", "orange", "blueberry", "grape", "strawberry" }; // First call to Where(): // Call Clump's Where() method with a predicate. ...