c# - 使用 LINQ 从不同的组中选择重复值

Question

我有一个如下所示的数据表，我想从其他类中选择重复的名称

Name    Class
Akbar   1B
Akbar   1B
Amar    1A
Amar    1C
Antoney 1A
Bindhu  1B
Bindhu  1D
John    1C
Raj     1B
Bindhu  2A

结果应该如下所示

Amar    1A
Amar    1C
Bindhu  1D
Bindhu  1B
Bindhu  2A

提前感谢任何指导

代码

var dtStudents = new DataTable();
dtStudents.Columns.Add("StudentID", typeof(int));
dtStudents.Columns.Add("StudentName", typeof(string));
dtStudents.Columns.Add("Class", typeof(string));
dtStudents.Columns.Add("ContactNo", typeof(string));

DataRow drStudent = dtStudents.NewRow();

drStudent["StudentID"] = 1;
drStudent["StudentName"] = "Akbar";
drStudent["Class"] = "1B";
drStudent["ContactNo"] = "989878679";
dtStudents.Rows.Add(drStudent);

dtStudents.Rows.Add(new object[] { 2, "Akabr", "1B", "989777" });
dtStudents.Rows.Add(new object[] { 3, "Amar", "1A", "3453" });
dtStudents.Rows.Add(new object[] { 4, "Amar", "1C", "543534" });
dtStudents.Rows.Add(new object[] { 5, "Antoney", "1A", "54345" });
dtStudents.Rows.Add(new object[] { 6, "Bindhu", "1B", "53453" });
dtStudents.Rows.Add(new object[] { 7, "Bindhu", "1D", "3453453" });
dtStudents.Rows.Add(new object[] { 8, "John", "1C", "3245345" });
dtStudents.Rows.Add(new object[] { 9, "Bindhu", "2A", "5345345" });

var results =
    from d in dtStudents.AsEnumerable()
    select d;

dataGridView1.DataSource = results.CopyToDataTable<DataRow>();

Answer 1

var results = dtStudents.AsEnumerable()
    .GroupBy(
        x => x.Field<string>("StudentName"), // group by student name
        (k, xs) => xs.GroupBy(
            x1 => x1.Field<string>("Class"), // group by class
            (k1, xs1) => xs1.First())) // if there are duplicates, take only the first
    .Where(x => x.Count() >= 2) // remove if student only has one class
    .SelectMany(x => x); // flatten back to a single collection

dataGridView1.DataSource = results.CopyToDataTable<DataRow>();