Class10.md

Class 10: Higher Order Markov Chains

Activities

• Code review implementations of hash table class instance methods
• Lecture and discussion on building higher order Markov chains with larger window sizes

Objectives

After completing this class session and the associated tutorial challenges, students will be able to ...

• Build higher order Markov chains based on observed frequency of n-grams (tuples of n words) in text
• Generate sentences by sampling words by performing random walks on higher order Markov chain
• Utilize a linked list as a queue to track words in a Markov chain's n-gram window

Resources

• Read Victor Powell's visual explanation of Markov chains and play with the interactive animated diagrams
• Read Alex Dejeu's article on how Markov chains work, with great examples specific to this project (especially section B, "Further Markov Model Topics" and its subsection 3, "Bigger Windows" on creating higher order Markov chains)
• Read Dataiku's article on using Markov chains with backoff to generate Donald Trump and Hillary Clinton quotes
• Watch Make School's Markov chains lecture
• Review Make School's Markov chains slides

Challenges

These challenges are the baseline required to complete the project and course. Be sure to complete these before next class session and before starting on the stretch challenges below.

• Page 11: Markov Chains Revisited
  • Build a second order Markov chain by analyzing frequency of adjacent words in text
  • Sample a random word from a state histogram in second order Markov chain
  • Generate a sentence by performing a random walk on second order Markov chain
• Page 12: Creating a Corpus
  • Choose a source with at least 20,000 words (ideally, well over 100,000 words)
  • Collect your corpus (use Diffbot corpus collection script if needed)

Stretch Challenges

These challenges are more difficult and help you push your skills and understanding to the next level.

• Page 11: Markov Chains Revisited
  • Extend code used to build second order Markov chain to build n-th order Markov chain for varying values of n (from 1 up to ~5)
  • Implement MarkovChain class to store states of word frequency histograms
    • Add methods for constructing state histograms and sampling words
  • Handle beginning and end of sentences with special start and stop tokens
  • Use a linked list as a queue to track words in Markov chain's n-gram window
  • Create a deque (double-ended queue) with a doubly-linked list
  • Implement a circular buffer (fixed-size queue) with a fixed-size array