C# 从数据表中删除列
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Remove columns from datatable
提问by Pradeep
I have a datatable with 20 columns. But i don't need all the columns for the current processing except 5. So i did the below to remove the columns
我有一个包含 20 列的数据表。但我不需要当前处理的所有列，除了 5. 所以我做了以下操作来删除列
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);
}
}
Instead of looping through the 15 times is there any other way to achieve using easily ?
除了循环 15 次之外，还有其他方法可以轻松实现使用吗？
回答by Waqar Janjua
Problem seems to be in your code, you get all the comlumns from the datatable then remove the columns but you have not again assign the columns to that datatable first you get columns
问题似乎出在您的代码中，您从数据表中获取所有comlumns，然后删除列，但您没有再次将列分配给该数据表，首先您获得了列
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
}
Try this
尝试这个
DataTable dt;
dt.Columns.Remove("columnName");
dt.Columns.RemoveAt(columnIndex);
you can use them as
你可以将它们用作
private void TestAndRemoveColumn(string dcName,DataTable datatable)
{
DataTable dt = datatable;
dt.Columns.Remove("dcName");
}
回答by Tim Schmelter
You could join the columns you want remove with the available columns:
您可以将要删除的列与可用列连接起来：
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());
If you know that you only have few remaining columns, you could add the column(s):
如果您知道只有几列剩余的列，则可以添加列：
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);
回答by Manjunath K Mayya
Alternatively you can select only the required columns(Only 5 in your case) like this.
或者，您可以像这样只选择所需的列（在您的情况下只有 5 个）。
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);
Hope this helps.
希望这可以帮助。
回答by SergeyA
In some scenarios may be preferable to clone DataTable and specify columns to copy.
在某些情况下，克隆 DataTable 并指定要复制的列可能更可取。
DataView view = new DataView(table);
DataTable table2 = view.ToTable(false, "clm6", "clm7", ...);
回答by K.Zelect
try this
尝试这个
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);
}
}
