在C＃中过滤DataTable

Question

I have a datatable like:

    ID | ID2
    --------
    1  |  2
    1  |  3
    12 |  2 
    15 |  3

I need to filter data table with ID2(I know two ID2 values in this case 2 and 3) in such a way that i should get output as

    ID | ID2
    --------
    1  |  2
    1  |  3

That means ID which have two ID2(2 and 3) should be selected.

dt.Select("ID2=2 AND ID2=3"); is not working in this case.

Thanks

Answer 1

It is not clear what are you searching for.
If you want to extract all the rows in which the same value for the ID column appears two or more times then

DataRow[] rows = dt.Select("Count(ID) > 1)")

You were right, this doesn't work on a datatable without relationships.
I have found a solution usig Linq,

// Returns an IGrouping<int,DataRow> for every ID that appears more than one time
var result = dt.AsEnumerable().GroupBy(z => z.Field<int>("ID"))
             .Select(q=> new{Count = q.Count(), ID=q.Key})
             .Where(x => x.Count > 1);

// Now we could extract the rows in the usual way
foreach(var l in result)
{
    DataRow[] r = dt.Select("ID=" + l.ID);
    r.Dump();
}

I don't know how efficient is this, but at least this seems to work

Answer 2

You can use LINQ to DataSet

var rows = table.AsEnumerable().Where(r => r.Field<int>("ID") == 1);             

BTW according to desired result you should filter by ID .