從數據表中刪除列

Question

我有一個包含 20 列的數據表。 但除了 5 之外，我不需要當前處理的所有列。所以我做了以下操作來刪除列

List<string> clmnames = new List<string>() { "clm6","clm7"..."clm20" };
foreach (string dcName in clmnames)
{
  TestAndRemoveColumn(dcName, ds.Tables["TestTable"]);
}


 private void TestAndRemoveColumn(string dcName,DataTable datatable)
 {
       DataColumnCollection dcCollection = datatable.Columns;
       if (dcCollection.Contains(dcName))
       {
           dcCollection.Remove(dcName);
       }
 }

除了循環 15 次之外，還有其他方法可以輕松實現使用嗎？

Answer 1

試試這個

List<string> listtoRemove = new List<string> { "CLM6", "CLM7", "CLM20" };
for (int i = dt.Columns.Count - 1; i >= 0; i--)
{
   DataColumn dc = dt.Columns[i];
   if (listtoRemove.Contains(dc.ColumnName.ToUpper()))
   {
       dt.Columns.Remove(dc);
   }
}

Answer 2

在某些情況下，克隆 DataTable 並指定要復制的列可能更可取。

DataView view = new DataView(table);
DataTable table2 = view.ToTable(false, "clm6", "clm7", ...);

Answer 3

問題似乎出在您的代碼中，您從數據表中獲取所有comlumns，然后刪除列，但您沒有再次將列分配給該數據表，首先您獲得了列

   DataColumnCollection dcCollection = datatable.Columns; // get cols
   if (dcCollection.Contains(dcName))
   {
       dcCollection.Remove(dcName); /// remove columns
     // but you have not updated you datatable columns.
        here should be something like this
       datatable.Columns = dcCollection; /// i don't know this will work or not check it
   }

試試這個

 DataTable dt;
 dt.Columns.Remove("columnName");
 dt.Columns.RemoveAt(columnIndex);

您可以將它們用作

private void TestAndRemoveColumn(string dcName,DataTable datatable)
{
    DataTable dt = datatable; 
    dt.Columns.Remove("dcName");      
}

Answer 4

或者，您可以像這樣只選擇所需的列（在您的情況下只有 5 個）。

        DataTable dt = new DataTable();
        dt.Columns.Add("ID");
        dt.Columns.Add("Value");

        dt.Rows.Add("1", "One");
        dt.Rows.Add("2", "Two");

        string[] arr= new string[1];
        arr[0] = "Value";//add the required columns to the array

        //return only the required columns.
        DataTable dt2 = dt.DefaultView.ToTable(false, arr);

希望這可以幫助。

Answer 5

您可以將要刪除的列與可用列連接起來：

var keepColNames = new List<String>(){ "clm5" };
var allColumns   = tbl.Columns.Cast<DataColumn>();
var allColNames  = allColumns.Select(c => c.ColumnName);
var removeColNames = allColNames.Except(keepColNames);
var colsToRemove = from r in removeColNames
                   join c in allColumns on r equals c.ColumnName
                   select c;
while (colsToRemove.Any())
    tbl.Columns.Remove(colsToRemove.First());

如果您知道只有幾列剩余的列，則可以添加列：

var colsToAdd = (from keepCol in keepColNames
                 join col in tbl.Columns.Cast<DataColumn>()
                 on keepCol equals col.ColumnName
                 select col).ToList();
tbl.Columns.Clear();
foreach (var colToAdd in colsToAdd)
    tbl.Columns.Add(colToAdd);