Merge Array based on Id using C# in ASP.Net

Hi yogesjoshi,

Please refer below sample and make changes according to your code.

Code

protected void Page_Load(object sender, EventArgs e)
{
    List<StudentDetail> studentDetails = new List<StudentDetail>();
    studentDetails.Add(new StudentDetail { Id = "1", SubjectDetails = new SubjectDetail { Key = "1", Value = "English" } });
    studentDetails.Add(new StudentDetail { Id = "1", SubjectDetails = new SubjectDetail { Key = "2", Value = "Math" } });
    studentDetails.Add(new StudentDetail { Id = "2", SubjectDetails = new SubjectDetail { Key = "2", Value = "Hindi" } });
    studentDetails.Add(new StudentDetail { Id = "3", SubjectDetails = new SubjectDetail { Key = "2", Value = "Science" } });

    List<Result> results = new List<Result>();
    string[] distinctId = studentDetails.Select(x => x.Id).Distinct().ToArray();
    foreach (string id in distinctId)
    {
        SubjectDetail[] subjects = studentDetails.Where(x => x.Id == id).Select(x => x.SubjectDetails).ToArray();
        results.Add(new Result { Id = id, SubjectDetails = subjects });
    }
}

public class Result
{
    public string Id { get; set; }
    public SubjectDetail[] SubjectDetails { get; set; }
}

public class StudentDetail
{
    public string Id { get; set; }
    public SubjectDetail SubjectDetails { get; set; }
}

public class SubjectDetail
{
    public string Key { get; set; }
    public string Value { get; set; }
}

Screenshot