LINQ GroupBy-按名称选择最低ID组

Question

I am trying to figure out how to select only the object with the lowest ID if the Name is the same:

public class BasicInfo
{
    public int Id {get;set;}
    public string Name {get; set;}
}

List<BasicInfo> BasicInfos = new List<BasicInfo>();
BasicInfos.Add(new BasicInfo() { Id = 1, Name = "John" });
BasicInfos.Add(new BasicInfo() { Id = 2, Name = "John" });

BasicInfos = BasicInfos.GroupBy(y => y.Name)...(What goes here?)

Answer 1

BasicInfos = BasicInfos.GroupBy(y => y.Name)
    .Select(y => y.OrderBy(z => z.Id).First())

Answer 2

Something like that :

BasicInfos = BasicInfos.GroupBy(y => y.Name)
                       .Select(y => new BasicInfo{ Name = y.Key, Id = y.Min(x => x.Id));

This will give you all names with the lowest key.

Answer 3

You can use MinBy from MoreLINQ :

var lowestIDsByName = BasicInfos.GroupBy(bi => bi.Name)
    .Select(g => g.MinBy(bi => bi.Id))
    .ToList();

Answer 4

List<BasicInfo> BasicInfos = new List<BasicInfo>();
BasicInfos.Add(new BasicInfo() { Id = 1, Name = "John" });
BasicInfos.Add(new BasicInfo() { Id = 2, Name = "John" });
BasicInfos.Add(new BasicInfo() { Id = 3, Name = "Sam" });
BasicInfos.Add(new BasicInfo() { Id = 4, Name = "Sam" });
BasicInfos.Add(new BasicInfo() { Id = 5, Name = "Igor" });
BasicInfos.Add(new BasicInfo() { Id = 6, Name = "joei" });

var usersWithSameName = BasicInfos.GroupBy(x => x.Name)
    .Where(x => x.Count() > 1)
    .Select(x => x.Single(y => y.Id == x.Min(z => z.Id)));

select only the object with the lowest ID if the Name is the same

So this returns just those where this a duplicate and if there is a duplicate then it returns the record with the smallest id. The above example would return 2 items and ignore those where no duplicate name could be found. If that is not correct then use this version without the where clause.

var usersWithSameName = BasicInfos.GroupBy(x => x.Name)
    .Select(x => x.Single(y => y.Id == x.Min(z => z.Id)));