C＃DataTable Linq选择列等于“ x”的不同值

Question

I have a Datatable (Groups) designed like so

ColumnA|ColumnB

X|Apple

Y|Purple

X|Apple

X|Mango

I basically want to select from columna where it's X and get the disinct from ColumnB

This is what I have

  var names = (from DataRow dr in Groups.Rows orderby (string)dr["ColumnB"] select (string)dr["ColumnB"]).Distinct(); 

This will give me distinct but it gives me Purple, and i dont want purple.

Thanks!

Answer 1

var names = (from DataRow dr in Groups.Rows
                 where dr["ColumnA"] == "X"
                 orderby (string)dr["ColumnB"]
                 select (string)dr["ColumnB"]).Distinct();

Answer 2

DataTable dt2 = dt1.Select("ColumnA = 'X'").CopyToDataTable().DefaultView.ToTable(true, "ColumnB");

So here we are selecting only the rows of data that you want, only rows where columnA is X. Then we choose only to see columnB, but with unique values only. Doing it in this order, you'll receive another datatable to play with. It'll only contain 1 column, columnB, and it'll only have unique/distinct values.

Enjoy.

Answer 3

If your return has more than one value and you want to Distinct the whole set by just one of the values you should use a custom IEqualityComparer .

var names = (from DataRow dr in Groups.Rows
             where (string)dr["ColumnA"] == "X"
             orderby (string)dr["ColumnB"]
             select new { 
                ColumnA = (string)dr["ColumnA"], 
                ColumnB = (string)dr["ColumnB"]
            }).Distinct(new MyCustomEqualityComparer());

edit: to include where clause

edit2: changed to custom IEqualityComparer