var functionDistinct = msaData.Select(x => new { x.Step, x.LogID }).Distinct().ToList().OrderBy(x => x.Step).ThenBy(x => x.LogID);

msaDataTable.Columns.Add("Time");
msaDataTable.Columns.Add("DUT");
msaDataTable.Columns.Add("Position");

//Add columns to datatable corresponding to each function. The number of columns is only known at runtime.
foreach (var item in functionDistinct)
{
    var column = new DataColumn() { DataType = typeof(double), ColumnName = String.Format("{0}-{1}", item.Step, item.LogID), AllowDBNull = true };

    msaDataTable.Columns.Add(column);
}

var distinctHeaderID = msaData.Select(x => x.HeaderID).Distinct();

foreach (var headerID in distinctHeaderID)
{
    ct.ThrowIfCancellationRequested();

    //Fetch the data for the current headerID
    var headerIDData = msaData.Where(x => x.HeaderID == headerID).Select(x => new { x.StartTime, x.DUT_id, x.printID, x.Step, x.LogID, x.Meas }).ToList();

    if (headerIDData != null)
    {
        DataRow row = msaDataTable.NewRow();

        row["Time"] = headerIDData.FirstOrDefault().StartTime;
        row["DUT"] = headerIDData.FirstOrDefault().DUT_id;
        row["Position"] = headerIDData.FirstOrDefault().printID;

        //Run through the data for the current headerID and assign the values to the right function.
        foreach (var data in headerIDData)
        {
            string function = String.Format("{0}-{1}", data.Step, data.LogID);
            row[function] = data.Meas;
        }

        msaDataTable.Rows.Add(row);
    }
}