Get a list of distinct values in List

Question

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 lt Note gt  Notes   new List lt Note gt       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

User · Accepted Answer

Notes Select x   gt  x Author  Distinct      This will return a sequence  IEnumerable lt string gt   of Author values -- one per unique value

User · Answer

mcilist    from mci in mcilist select mci  Distinct   ToList

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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 lt KeyNote gt  KeyNotes   get  set    public List lt RefCourse gt  GetCourses   get  set         List lt RefCourse gt  courses   KeyNotes Select x   gt  new RefCourse   CourseId   x CourseId  Name   x CourseName    Distinct   ToList      By using the above logic  we can get the unique Courses

User · Answer

Distinct the Note class by Author  var DistinctItems   Note GroupBy x   gt  x Author  Select y   gt  y First      foreach var item in DistinctItems          Add to other List

User · Answer

Jon Skeet has written a library called morelinq which has a DistinctBy   operator  See here for the implementation  Your code would look like  IEnumerable lt Note gt  distinctNotes   Notes DistinctBy note   gt  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   gt  i Name  DistinctBy i   gt  i ProductId  ToList

[c#] Get a list of distinct values in List

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