从列表中返回元组计数

Question

List<Tuple<string, string, int>> roads

roads.Add(new Tuple<string, string, int>)("first", "second", 1);
roads.Add(new Tuple<string, string, int>)("first", "second", 2);
roads.Add(new Tuple<string, string, int>)("first", "second", -5);
roads.Add(new Tuple<string, string, int>)("first", "second", 3);

需要show count元组，其中item3＆lt; 0

我的变种（不正确）：

var r roads.Select(t => t.Item3 < 0).Count;

Answer 1

Linq提供Count方法的重载，它接受Func<T, bool>并计算符合该条件的元素数量：

int countLessThanZero = roads.Count(t => t.Item3 < 0);

或者，您可以先筛选列表，然后计算筛选列表中元素的数量：

int countLessThanZero = roads.Where(t => t.Item3 < 0).Count();