c# - 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);

需要显示 item3 < 0 的计数元组

我的变体(不正确):

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

Answer 1

Linq 提供了 Count 的重载采用 Func<T, bool> 的方法并将计算满足该条件的元素的数量:

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

或者，您可以先过滤列表，然后计算过滤列表中的元素数:

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