What I usually do, is check for the existence of my output file. If it exists, I simple open it and append to the end, but if not, I then create the file and add the header.
Obviously, you would have to remember to delete the file before starting optimization.
Alternatively, don't delete it and actually accumulate the various group runs when you are evaluating various combinations. That way you can make a global analysis of various run groupings you may have executed.
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