So do you mean that somehow you will check all of the data values in all of the columns, looking for those columns which do not contain any values at all, and then unmap those columns?
That would require reading the file twice and (I would guess) would take longer than just leaving the blanks in there.
If you haven't even tried to resolve your issue, please don't expect the hard-working volunteers here to waste their time providing links to answers which you could easily have found yourself.