Learning Data Mining with Python

Chapter 12
One problem with using log probabilities is that they don't handle zero values well
(although, neither does multiplying by zero probabilities). This is due to the fact
that log(0) is undefined. In some implementations of Naive Bayes, a 1 is added to
all counts to get rid of this, but there are other ways to address this. This is a simple
form of smoothing of the values. In our code, we just return a very small value if the
word hasn't been seen for our given gender.
Back to our prediction function, we can test this by copying a post from our dataset:
new_post = """ Every day should be a half day. Took the afternoon
off to hit the dentist, and while I was out I managed to get my oil
changed, too. Remember that business with my car dealership this
winter? Well, consider this the epilogue. The friendly fellas at the
Valvoline Instant Oil Change on Snelling were nice enough to notice
that my dipstick was broken, and the metal piece was too far down in
its little dipstick tube to pull out. Looks like I'm going to need a
magnet. Damn you, Kline Nissan, daaaaaaammmnnn yooouuuu.... Today
I let my boss know that I've submitted my Corps application. The news
has been greeted by everyone in the company with a level of enthusiasm
that really floors me. The back deck has finally been cleared off
by the construction company working on the place. This company, for
anyone who's interested, consists mainly of one guy who spends his
days cursing at his crew of Spanish-speaking laborers. Construction
of my deck began around the time Nixon was getting out of office.
"""
We then predict with the following code:
nb_predict(model, new_post)
The resulting prediction, male, is correct for this example. Of course, we never test a
model on a single sample. We used the file starting with 51 for training this model.
It wasn't many samples, so we can't expect too high of an accuracy.
The first thing we should do is train on more samples. We will test on any file that
starts with a 6 or 7 and train on the rest of the files.
In the command line and in your data folder (cd