c# - 连接两个集合，从第二个集合中获取值(左外连接)

Question

假设我有两个 List<KeyValuePair<string, string>> a 和 b，其中 a =

"one", "N",
"two", "N",
"three", "N"

和b =

"one", "Y"
"two", "N"

我想做一个左外连接，但从 Value 的 b 中获取值如果b中有一个条目，那么结果应该是=

"one", "Y" <- this value is taken from b
"two", "N",
"three", "N"

我尝试过进行正常的左外连接，但结果为 Value “三”始终是空字符串

    var res = (from l in a
              join r in b on l.Key equals r.Key into lrs
              from lr in lrs.DefaultIfEmpty()
              select new KeyValuePair<string, string>(l.Key, lr.Value)).ToArray();

Answer 1

这也应该有效:

var res = (from p in b.Concat(a)
           group p by p.Key into g
           select g.First()).ToArray();

或者用流畅的语法:

var res = b.Concat(a).GroupBy(p => p.Key, (k, g) => g.First()).ToArray();