Refactoring - Speed increase

Question

How can I make this function more efficient. It's currently running at 6 - 45 seconds. I've ran dotTrace profiler on this specific method, and it's total time is anywhere between 6,000ms to 45,000ms. The majority of the time is spent on the "MoveNext" and "GetEnumerator" calls.

and example of the times are

71.55% CreateTableFromReportDataColumns - 18, 533* ms - 190 calls
 -- 55.71% MoveNext - 14,422ms - 10,775 calls 

can I do to speed this method up? it gets called a lot, and the seconds add up:

    private static DataTable CreateTableFromReportDataColumns(Report report)
    {
        DataTable table = new DataTable();
        HashSet<String> colsToAdd = new HashSet<String> { "DataStream" };
        foreach (ReportData reportData in report.ReportDatas)
        {
            IEnumerable<string> cols = reportData.ReportDataColumns.Where(c => !String.IsNullOrEmpty(c.Name)).Select(x => x.Name).Distinct();

            foreach (var s in cols)
            {
                if (!String.IsNullOrEmpty(s))
                    colsToAdd.Add(s);
            }
        }

        foreach (string col in colsToAdd)
        {
            table.Columns.Add(col);
        }

        return table;
    }

If you need the sql table definitions here they are:

ReportData

ReportID            int

ReportDataColumn

ReportDataColumnId  int
ReportDataId        int 
Name                varchar(255)    
Value               text    

Answer 1

I believe you should be able to simplify your function into something like this

var columnsToAdd = report.ReportDatas
                    .SelectMany(r => r.ReportDataColumns)
                    .Select(rdc => rdc.Name)
                    .Distinct()
                    .Where(name => !string.IsNullOrEmpty(name));

And from there add the names to your table.

Answer 2

Your code (only) runs foreach loops so the conclusion that the method spends most of its time in MoveNext() et al is not so surprising.

You are doing double work on both the isnullOrEmpty and the Distinct (is repeated by the HashSet).

My version would be:

private static DataTable CreateTableFromReportDataColumns(Report report)
{
    DataTable table = new DataTable();
    HashSet<String> colsToAdd = new HashSet<String> { "DataStream" };
    foreach (ReportData reportData in report.ReportDatas)
    {

        foreach (var column in reportData.ReportDataColumns)
        {
            if (!String.IsNullOrEmpty(column.Name))
                colsToAdd.Add(column.Name);
        }
    }

    foreach (string col in colsToAdd)
    {
        table.Columns.Add(col);
    }

    return table;
}

But I don't expect a huge improvement