.NET Framework聚合（折叠）
示例
在每个步骤中生成一个新对象：
var elements = new[] {1,2,3,4,5};
var commaSeparatedElements = elements.Aggregate(
seed: "",
func: (aggregate, element) => $"{aggregate}{element},");
Console.WriteLine(commaSeparatedElements); //1,2,3,4,5,在所有步骤中使用同一对象：
var commaSeparatedElements2 = elements.Aggregate(
seed: new StringBuilder(),
func: (seed, element) => seed.Append($"{element},"));
Console.WriteLine(commaSeparatedElements2.ToString()); //1,2,3,4,5,使用结果选择器：
var commaSeparatedElements3 = elements.Aggregate(
seed: new StringBuilder(),
func: (seed, element) => seed.Append($"{element},"),
resultSelector: (seed) => seed.ToString());
Console.WriteLine(commaSeparatedElements3); //1,2,3,4,5,如果省略种子，则第一个元素成为种子：
var seedAndElements = elements.Select(n=>n.ToString());
var commaSeparatedElements4 = seedAndElements.Aggregate(
func: (aggregate, element) => $"{aggregate}{element},");
Console.WriteLine(commaSeparatedElements4); //12,3,4,5,