相当于SELECT DISTINCT的LINQ

Question

I'm wanting to only display a list of CourseNo with no duplicates using LINQ, but I can't quite figure the syntax out.

        this.Distinct_CourseNo = (from c in Roster_Sections
                                  select c).Distinct(CourseNo).ToList;

The SQL equivalent would be something along the lines of:

SELECT DISTINCT CourseNo
FROM Roster_Sections

Answer 1

using select c will include all columns in the Roster_Sections , thus Distinct() will not work if atleast one row in a column is different from the other row.

this.Distinct_CourseNo = (from c in Roster_Sections
                          select c.CourseNo).Distinct().ToList();

or

this.Distinct_CourseNo = Roster_Sections.Distinct(c => c.CourseNo).ToList();

Answer 2

All the provided answers are applicable only if you have moreLINQ . However, you can try this instead:

this.Distinct_CourseNo = (from c in Roster_Sections
                          group c by c.CourseNo into g
                          select g.First()).ToList();

Answer 3

You'd pass Distinct a lambda describing what defines distinctness:

this.Distinct_CourseNo = Roster_Sections.Distinct(x => x.CourseNo).ToList();

If you mean to get a list of unique course numbers as opposed to a list of unique courses based off course number, 今 草 顿 웃's answer is the way to go.