This is an implemenation of a very trivial, and very costly algorithm to find Similarity in a collection of items. It calculates a distance between the length of the items compressed each on its own, and compressed when concatenated The theory is sound.

Add this line to your application's Gemfile:

gem 'simple_similarity'

And then execute:

$ bundle

Or install it yourself as:

$ gem install simple_similarity

Get the distance between "Hello" and "World", always takes to arguments.

SimpleSimilarity::SimpleSimilarity.distance("Hello","World")

$ 0.125

SimpleSimilarity::SimpleSimilarity.case_insensitive_distance("Hello","hello")

$ 1.0

Get a distance matrix, the first argument is an array of elements, the second is a cutoff ratio for the detected similarities (0.5 is quite similar, above 0.8 we are basically identical, depending on the length of the original strings..)

 SimpleSimilarity::SimpleSimilarity.distance_matrix(%w( hello, hell, world), 0.5, true, false)

 $  => {
 :matrix=>[
 [nil, 0.5833333333333333, 0.11764705882352944], 
 [nil, nil, 0.125], 
 [nil, nil, nil]
 ], 
 :similar_terms=>[{
 :first_term=>[0, "hello,"], 
 :second_term=>[1, "hell,"], 
 :score=>0.5833333333333333}]} 

1. The algorithm for calculating the distance matrix costs (n^2/2) - n in time and n^2 in memory

So if n = 100,000 there will be 4,999,900,000 calculations (and each is very expensive.. we are zipping)

2. setting only_hits to true does not return the matrix only the hits but optimizes memory usage.

the matrix can be used later for clustering....

#Testing spec:

bundle exec rspec spec         

Benchmark:

On my machine comparing 100 items takes around 8 seconds, comaring 1000 items around 20 minutes...:

bundle exec ruby spec/benchmark.rb

If what you want to compare are longer documents, swap the

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request