Minimum Term Frequency Change

Change the Minimum Term Frequency from 1 to 2.

I am pretty sure this removes terms that only appear once, and a term
has to appear at least twice to be a word in the bag. It speeds up the
program significantly and makes the arff files a lot smaller.

-M 1 (default)
Training Data: 1.01 gb
Test Data : 376 mb

-M 2
Training Data: 407 mb
Test Data : 147 mb