Class: Nanoc::Core::DirectedGraph

Inherits:
Object
  • Object
show all
Defined in:
lib/nanoc/core/directed_graph.rb

Overview

Represents a directed graph. It is used by the dependency tracker for storing and querying dependencies between items.

Examples:

Creating and using a directed graph


# Create a graph with three vertices
graph = Nanoc::Core::DirectedGraph.new(%w( a b c d e f g ))

# Add edges
graph.add_edge('a', 'b')
graph.add_edge('b', 'c')
graph.add_edge('b', 'f')
graph.add_edge('b', 'g')
graph.add_edge('c', 'd')
graph.add_edge('d', 'e')

# Get (direct) predecessors
graph.direct_predecessors_of('b').sort
  # => %w( a )

# Modify edges
graph.delete_edges_to('c')

# Get (direct) predecessors again
graph.direct_predecessors_of('e').sort
  # => %w( d )

Constant Summary collapse

EMPTY_SET = 
Set.new.freeze

Creating a graph collapse

Modifying the graph collapse

Querying the graph collapse

Constructor Details

#initialize(vertices) ⇒ DirectedGraph

Creates a new directed graph with the given vertices.



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# File 'lib/nanoc/core/directed_graph.rb', line 37

def initialize(vertices)
  @vertex_to_idx_map = {}
  @vertices = []
  @next_vertex_idx = 0
  vertices.each do |v|
    @vertices << v
    @vertex_to_idx_map[v] = @next_vertex_idx
    @next_vertex_idx += 1
  end

  @to_graph = {}
  @from_graph = {}

  @edge_props = {}
end

Instance Method Details

#add_edge(from, to, props: nil) ⇒ void

This method returns an undefined value.

Adds an edge from the first vertex to the second vertex.

Parameters:

  • from —

    Vertex where the edge should start

  • to —

    Vertex where the edge should end



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# File 'lib/nanoc/core/directed_graph.rb', line 77

def add_edge(from, to, props: nil)
  add_vertex(from)
  add_vertex(to)

  @to_graph[to] ||= Set.new
  @to_graph[to] << from

  @from_graph[from] ||= Set.new
  @from_graph[from] << to

  if props
    @edge_props[[from, to]] = props
  end
end

#add_vertex(vertex) ⇒ void

This method returns an undefined value.

Adds the given vertex to the graph.

Parameters:

  • vertex —

    The vertex to add to the graph



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# File 'lib/nanoc/core/directed_graph.rb', line 97

def add_vertex(vertex)
  return if @vertex_to_idx_map.key?(vertex)

  @vertices << vertex
  @vertex_to_idx_map[vertex] = @next_vertex_idx
  @next_vertex_idx += 1
end

#delete_edges_to(to) ⇒ void

This method returns an undefined value.

Deletes all edges going to the given vertex.

Parameters:

  • to —

    Vertex to which all edges should be removed



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# File 'lib/nanoc/core/directed_graph.rb', line 110

def delete_edges_to(to)
  return if @to_graph[to].nil?

  @to_graph[to].each do |from|
    @edge_props.delete([from, to])
    @from_graph.delete(from)
  end
  @to_graph.delete(to)
end

#direct_predecessors_of(to) ⇒ Array

Returns the direct predecessors of the given vertex, i.e. the vertices x where there is an edge from x to the given vertex y.

Parameters:

  • to —

    The vertex of which the predecessors should be calculated

Returns:

  • (Array) —

    Direct predecessors of the given vertex



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# File 'lib/nanoc/core/directed_graph.rb', line 128

def direct_predecessors_of(to)
  @to_graph.fetch(to, EMPTY_SET)
end

#direct_successors_of(from) ⇒ Object 



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# File 'lib/nanoc/core/directed_graph.rb', line 132

def direct_successors_of(from)
  @from_graph.fetch(from, EMPTY_SET)
end

#edges ⇒ Array

Returns an array of tuples representing the edges. The result of this method may take a while to compute and should be cached if possible.

Returns:

  • (Array) —

    The list of all edges in this graph.



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# File 'lib/nanoc/core/directed_graph.rb', line 149

def edges
  result = []
  @vertices.each_with_index do |v2, i2|
    direct_predecessors_of(v2)
      .map { |v1| [@vertex_to_idx_map[v1], v1] }
      .each do |i1, v1|
        result << [i1, i2, @edge_props[[v1, v2]]]
      end
  end
  result
end

#inspect ⇒ Object 



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# File 'lib/nanoc/core/directed_graph.rb', line 53

def inspect
  s = []

  @vertices.each do |v2|
    direct_predecessors_of(v2).each do |v1|
      s << [
        "#{v1.inspect} -> #{v2.inspect} " \
        "props=#{@edge_props[[v1, v2]].inspect}",
      ]
    end
  end

  "#{self.class}(#{s.join(', ')})"
end

#props_for(from, to) ⇒ Object 



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# File 'lib/nanoc/core/directed_graph.rb', line 136

def props_for(from, to)
  @edge_props[[from, to]]
end

#vertices ⇒ Array

Returns The list of all vertices in this graph.

Returns:

  • (Array) —

    The list of all vertices in this graph.



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# File 'lib/nanoc/core/directed_graph.rb', line 141

def vertices
  @vertices
end