Class: TextRank::GraphStrategy::Coocurrence

Inherits:
Object
  • Object
show all
Defined in:
lib/text_rank/graph_strategy/coocurrence.rb

Overview

The original TextRank algorithm uses co-occurrence in determining how to construct a graph of eligible token keywords and relate them together. Given a window size of N any other token at most N positions away from a token is considered co-ocurrent, and an edge will be drawn between them.

This implementation makes a slight change from the original algorithm by choosing a weight of 1/distance_from_token as the edge weight.

= Example Coocurrence.new(ngram_size: 4).build_graph(%w[what a pessimist you are exclaimed candide], graph) # graph.add("what", "a", 1.0) # graph.add("what", "pessimist", 0.5) # graph.add("what", "you", 0.3333333333333333) # graph.add("what", "are", 0.25) # graph.add("a", "what", 1.0) # graph.add("a", "pessimist", 1.0) # graph.add("a", "you", 0.5) # graph.add("a", "are", 0.3333333333333333) # graph.add("a", "exclaimed", 0.25) # graph.add("pessimist", "what", 0.5) # graph.add("pessimist", "a", 1.0) # graph.add("pessimist", "you", 1.0) # graph.add("pessimist", "are", 0.5) # graph.add("pessimist", "exclaimed", 0.3333333333333333) # graph.add("pessimist", "candide", 0.25) # graph.add("you", "what", 0.3333333333333333) # graph.add("you", "a", 0.5) # graph.add("you", "pessimist", 1.0) # graph.add("you", "are", 1.0) # graph.add("you", "exclaimed", 0.5) # graph.add("you", "candide", 0.3333333333333333) # graph.add("are", "what", 0.25) # graph.add("are", "a", 0.3333333333333333) # graph.add("are", "pessimist", 0.5) # graph.add("are", "you", 1.0) # graph.add("are", "exclaimed", 1.0) # graph.add("are", "candide", 0.5) # graph.add("exclaimed", "a", 0.25) # graph.add("exclaimed", "pessimist", 0.3333333333333333) # graph.add("exclaimed", "you", 0.5) # graph.add("exclaimed", "are", 1.0) # graph.add("exclaimed", "candide", 1.0) # graph.add("candide", "pessimist", 0.25) # graph.add("candide", "you", 0.3333333333333333) # graph.add("candide", "are", 0.5) # graph.add("candide", "exclaimed", 1.0)

Instance Method Summary collapse

Constructor Details

#initialize(ngram_size: 3, **_) ⇒ Coocurrence

Returns a new instance of Coocurrence.

Parameters:

  • ngram_size (Fixnum) (defaults to: 3) —

    Window size around a token considered co-occurrence



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# File 'lib/text_rank/graph_strategy/coocurrence.rb', line 54

def initialize(ngram_size: 3, **_)
  @ngram_size = ngram_size
end

Instance Method Details

#build_graph(tokens, graph) ⇒ Object

Build a graph for which the PageRank algorithm will be applied return [nil]

Parameters:

  • tokens (Array<String>) —

    filtered tokens from which to build a graph

  • graph (PageRank::Base) —

    a PageRank graph into which to add nodes/edges



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# File 'lib/text_rank/graph_strategy/coocurrence.rb', line 62

def build_graph(tokens, graph)
  ngram_window = (@ngram_size * 2) + 1
  tokens.size.times do |i|
    ngram_window.times do |j|
      consider_ngram_window(tokens, graph, i, j)
    end
  end
  nil
end