I’ve had a bunch of beer reviews and ratings data sitting on my hard drive for about year. For a beer nerd like me, that’s a pretty cool dataset, yet I’ve let it collect digital dust.
Fast forward to last week, where somehow I wound up in the Wikipedia Death Spiral. You know what I mean - you click a link to a Wikipedia article, that article takes you to a new one, then you’re on another, and another … we’ve all been there. And it’s kind of awesome.
Well, the rabbit hole led me to Markov chains, which seemed like a good excuse to mess around with that beer review data.
What are Markov chains?
Markov chains are a random process that transitions to various states, where the “next state” is based on its probability distribution, given the current state.
Imagine we have the following sequence of days, where S indicates it was sunny and R indicates it was rainy:
S S R R S R S S R R R R S R S S S R
Let’s pick a random beginning “state” - let’s just say it’s S (sunny). The next state is based only on the current state. Since our current state is S, we only need to look at observations immediately following a sunny day.
To illustrate, let’s look at the weather pattern again, this time putting the observations to be considered in bold.
S S R R S R S S R R R R S R S S S R
Even though there are 18 observations, only nine need to be considered for the possible next state. Of the nine, four are S and five are R, giving us a 44% (4/9) chance of the next state being sunny and a 55% (5/9) chance of it being rainy.
Now, let’s assume our beginning state (S) transitioned to a second state of R (which it had a 55% chance of doing). Here are the states we need to consider for the possible third state:
S S R R S R S S R R R R S R S S S R
There’s an equal chance (4/8) the third state will be S or R.
With a second-order Markov chain, the current state is two observations. Let’s assume a beginning state of SR and use the same weather sequence as above, again putting the possible next states in bold.
S S R R S R S S R R R R S R S S S R
This time there are only four observations to consider as possible “next states,” with an equal chance it’ll be S or R.
Let’s assume the “next state” picked is R. Now our current (second) state is RR - the S from our beginning state is forgotten. The following are possible third states:
S S R R S R S S R R R R S R S S S R
Again, there’s an equal chance of our third state being S or R.
We can continue picking “next states” and eventually we’ll have generated a random, yet probabilistic sequence of weather.
These same principles can be used to generate a sentence from text data - pick a random beginning state (word) from the text and then pick the next word based on the likelihood of it occurring, given the current word. A first-order Markov sentence would have a one word current state, a second-order would have a two word current state, … and so on.
The larger the corpus and the higher the order, the more sense these Markov generated sentences make. Good thing I have a lot of beer reviews.
The (mini) project
This seemed ripe for a Twitter bot, so I created BeerSnobSays, which tweets nonsensical beer reviews generated via second-order Markov chains.
Not everything it tweets makes much sense:
dissipates about a finger of head and some mild spice interwoven and even beer at a local Greek restaurant.
a big thumbs up though and there are plenty other choices that I was really no distinguishing characteristics that stand out.
those who are looking for a beer best characteristic of this beer into the hype and the lager style that is unwelcome.
But some of it is pretty funny:
off by itself, the taste of apple juice colored brew with a nice warming alcohol bathes your noodle in its dryness.
is almost like sour grains with a hint of booze in the finish, with sweet orange peels and pine sap.
a charred woodiness and smoke can run into pineapple, oranges and citrusy oils with a clean alcohol sting at the bottom of the recipe.
the berry aspect is evident but the tartness and dryness from the beer starts off surprisingly pleasant.
I’m not sure if that last one’s from the bot or a famous poet.
You can follow me and BeerSnobSays on Twitter. You can also find the code for the bot on GitHub.