Question

I have a List<String> that has allowed columns. and I have a dataset DT1 which has all the columns listed . Now that i want to do is to only get allowed columns from DT1.

List<String> = FirstName,LastName,Age,EmailAddress
DT1 contains = FirstName,LastName,Age,EmailAddress,Sex,PhoneNumber,Address

I have already tried DataTable.Merge() , foreach etc… but i couldn’t get my expected result.

Answer 1

Assuming your list is a List<String> containing the column names:

var toBeRemoved = DT1.Columns.Cast<DataColumn>()
                 .Where(c => !allowed.Contains(c.ColumnName))
                 .ToList();
foreach(DataColumn col in toBeRemoved)
{
     DT1.Columns.Remove(col);
}

Edit: You wanted to know how to set fields null which are in the removelist:

foreach(DataRow row in DT1.Rows) 
{
    foreach(DataColumn col in toBeRemoved)
    {
        row[col] = DBNull.Value;
    }
}