DataRow[] row = table.Select("Weight='57'");//  has  1  record
  DataTable dt = new DataTable();

     foreach (DataRow dr in row)
                {
                    dt.ImportRow(dr);
                }
                dt.AcceptChanges();

DataTable dtDest = new DataTable();
dtDest = dsActivity.Tables[0].Clone();
foreach(DataRow dr in dsSrc.Tables[0].Rows)
{
 DataRow newRow = dtDest .NewRow();
 newRow.ItemArray = dr.ItemArray;
 dtDest.Rows.Add(newRow);
}

DataRow[] rows = table.Select("Weight='57'");
DataTable dt = new DataTable();

foreach (DataRow item in rows)
{
    // add values into the datatable
    dt.Rows.Add(item.ItemArray);
}

dt.Rows.Add(dr)

DataTable DT = DTMain.Clone();
// suppose DT is the table where we need to put datarows and DTMain is a table
// having the stucture of the datatbale, means you must have some structure for
// datatable.

//supposes you have a collection of datarows as

foreach(DataRow dr in DatarRowColl)
{
    DT.ImportRow(dr);
}

DT.AcceptChanges();

// here you get the datarows in a datatable.

DataTable dt = new DataTable();

DataRow[] dr = dt.Select("Your string");

DataTable dt1 = dr.copyToDataTable();