In C#, say I have a class called Note with three string member variables.
public class Note{public string Title;public string Author;public string Text;}And I have a list of type Note:
List<Note> Notes = new List<Note>();What would be the cleanest way to get a list of all distinct values in the Author column?
I could iterate through the list and add all values that aren't duplicates to another list of strings, but this seems dirty and inefficient. I have a feeling there's some magical Linq construction that'll do this in one line, but I haven't been able to come up with anything.
Best Answer
Notes.Select(x => x.Author).Distinct();This will return a sequence (IEnumerable<string>) of Author values -- one per unique value.
Distinct the Note class by Author
var DistinctItems = Notes.GroupBy(x => x.Author).Select(y => y.First());foreach(var item in DistinctItems){//Add to other List}Jon Skeet has written a library called morelinq which has a DistinctBy() operator. See here for the implementation. Your code would look like
IEnumerable<Note> distinctNotes = Notes.DistinctBy(note => note.Author);Update: After re-reading your question, Kirk has the correct answer if you're just looking for a distinct set of Authors.
Added sample, several fields in DistinctBy:
res = res.DistinctBy(i => i.Name).DistinctBy(i => i.ProductId).ToList();public class KeyNote{public long KeyNoteId { get; set; }public long CourseId { get; set; }public string CourseName { get; set; }public string Note { get; set; }public DateTime CreatedDate { get; set; }}public List<KeyNote> KeyNotes { get; set; }public List<RefCourse> GetCourses { get; set; } List<RefCourse> courses = KeyNotes.Select(x => new RefCourse { CourseId = x.CourseId, Name = x.CourseName }).Distinct().ToList();By using the above logic, we can get the unique Courses.
@if (dataModal.Count > 0){var DistinctItems = dataModal.GroupBy(x => x.Year).Select(y => y.First());<div class="col-md-3"><label class="fs-7 form-label text-muted">@Localizer["Year"]</label><InputSelect id="ddlYears" class="form-select" @bind-Value="filter.Year"> <option value="">@Localizer["Select"]</option>@foreach (var year in DistinctItems){<option value="@year.Year">@year.Year</option>}</InputSelect></div>}mcilist = (from mci in mcilist select mci).Distinct().ToList();