Writing a text file during data collection can only be performed by adding rows to the file, not columns.
However, there are 3 common alternatives. First, write the data directly to Excel using ActiveX. Second, keep all data in memory until the test is complete, then transpose the data before writing (dangerous). Third, write all data to text file row by row, and at the completion of the test, read back the data file, transpose it and write it back to another file.
Michael