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Various distance and similarity measures for machine learning.


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A gem to test what metric is best for certain kinds of datasets in machine learning. Besides the Array class, I also want to support NMatrix.

This is a fork of the gem Distance Measure, which has a similar objective, but isn't actively maintained and doesn't support NMatrix. Thank you, @reddavis. :)


gem install measurable

This gem is currently being tested on MRI Ruby 1.9.3, 2.0, 2.1.0, 2.1 (HEAD) and on Rubinius 2.x (HEAD). I hope to add JRuby support in the future.

Available distance measures

I'm using the term "distance measure" without much concern for the strict mathematical definition of a metric. If the documentation for one of the methods isn't clear about it being or not a metric, please open an issue.

The following are the similarity measures supported at the moment:

How to use

The API I intend to support is something like this:

require 'measurable'

# Calculate the distance between two points in space.
Measurable.euclidean([1, 1], [0, 0]) # => 1.41421

# Calculate the norm of a vector, i.e. its distance from the origin.
Measurable.euclidean([1, 1]) # => 1.4142135623730951

# Get the cosine distance between
Measurable.cosine_distance([1, 2], [2, 3]) # => 0.007722123286332261

# Calculate sum of squares directly.
Measurable.euclidean_squared([3, 4]) # => 25

Most of the methods accept arbitrary enumerable objects instead of Arrays. For example, it's possible to use NMatrix.


The documentation is hosted on rubydoc.


See LICENSE for details.

The original distance_measures gem is copyrighted by @reddavis.

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