How to delete columns effciently without Spotfire freezing?

  Can you please find out from somebody in Spotfire dev group whether there is a better way of doing the following, ( BTW it used to be instantaneous in 7.0 but very slow in 7,11)

dt = getDataTable(newTableName)

if dt != None and SourceTable.RowCount > 0:

                dataTableDataSource = DataTableDataSource(SourceTable)

                dt.ReplaceData(dataTableDataSource)

                rowcount = dt.RowCount

                columns=dt.Columns

                for column in dt.Columns:

                                if (column.RowValues.InvalidRows.Count == rowcount and column.Name != 'Samples_Tag' ):

                                                columns.Remove(column)

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