如何按两个字段分组并返回匹配的原始对象？

Question

任何人都可以告诉我，在这些尝试通过Linq找到重复的名字和姓氏时我会搞砸了什么？

//尝试1

var  duplicateName =  
    from o in people
    from x in people 
    group o by new { Last= x.LastName?.Trim()?.ToUpperInvariant(),  First=x.FirstName?.Trim()?.ToUpperInvariant() }
    into g
    where g.Count() > 1
    select g; 

//尝试2

var  duplicateName =  
        people.GroupBy(x => new { Last= x.LastName?.Trim()?.ToUpperInvariant(),  First=x.FirstName?.Trim()?.ToUpperInvariant() })
        .Where(g=> g.Count() > 1) 
        .Select(y => y)
        .ToList() ;

Answer 1

第二次尝试几乎就是你想要的。但是你选择了分组。如果要选择分组中的对象，则应使用SelectMany：

var  duplicateName =  
        people.GroupBy(x => new { Last= x.LastName?.Trim()?.ToUpperInvariant(),  First=x.FirstName?.Trim()?.ToUpperInvariant() })
        .Where(g=> g.Count() > 1) 
        .SelectMany(y => y)
        .ToList() ;