ruby-knn

Simple kNN Classifier written in Ruby

Usage

Bundle the gem in your project and follow the instructions below.

# Gemfile
gem 'knn', git: '[email protected]:jonmidhir/ruby-knn.git'

# Elsewhere
require 'knn'

Or you can start messing about right away by cloning this project and running

./bin/console

Vector

Vectors are arrays of components, representing features, where the first element is a label. An example looks like:

['vegetable', 0, 1, 0, 1, 0, 0, 0]

Calculating distance between vectors

Distance Calculators can be used to determine the distance between two vectors according to different algorithms. The vectors can be any length but when comparing two the lengths must match.

The Squared Euclidean distance between two vectors can be calculated like so:

vector1 = [nil, 1, 2]
vector2 = [nil, 0, 0]

SquaredEuclideanCalculator.new.distance(vector1, vector2)
#> 2.23606797749979

The distance is always a positive, floating-point number.

Classifier

The Knn::Classifier takes an array of vectors (of the same length), representing the training data, a value for k, the number of neighbours used to classify a data point, and an optional distance calculator class.

By default, the squared Euclidean distance is used because this produces the same accuracy as Euclidean without requiring the expensive square root calculation.

vectors = [
  ['apple', 1, 2],
  ['orange', 5, 5],
  ['apple', 0, 2],
  ['orange', 7, 5],
  ['apple', 1, 1],
  ['orange', 6, 5]
] # ...

classifier = Knn::Classifier.new(vectors, 3, distance_calculator = SquaredEuclideanCalculator)

new_datapoint = [nil, 2,2]

classifier.classify(new_datapoint)
#> 'apple'

If you wish you can inspect the nearest neighbours that produced this result:

classifier.nearest_neighbours_to(new_datapoint)

Handwriting Example

As mentioned vectors of any size can be used and the example provided in /examples is taken from Machine Learning in Action by @pbharrin (https://github.com/pbharrin/machinelearninginaction).

To run the entire test on the 946 examples takes around 15 minutes on a decent machine:

./example/bin/test

You can also start the console, which loads the environment and provides you with a 'pre-trained' variable @knn_classifier to test individual characters against.

./example/bin/console