Module: Paths

Defined in:
lib/scout/network/paths.rb

Class Method Summary collapse

Class Method Details

.breadth_first(adjacency, sources, max_steps = nil) ⇒ Object

New: breadth‑first exploration from one or many start nodes (unweighted) adjacency: Hash[String => Array] sources: String or Array max_steps: Integer or nil (no limit) Returns Hash[node => distance_from_any_source]



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# File 'lib/scout/network/paths.rb', line 145

def self.breadth_first(adjacency, sources, max_steps = nil)
  sources = [sources] unless Array === sources
  distances = {}
  queue = []

  sources.each do |s|
    next unless adjacency.include?(s)
    distances[s] = 0
    queue << s
  end

  until queue.empty?
    u = queue.shift
    d = distances[u]
    next if max_steps && d >= max_steps
    next unless adjacency.include?(u)
    adjacency[u].each do |v|
      next if distances.key?(v)
      distances[v] = d + 1
      queue << v
    end
  end

  distances
end

.dijkstra(adjacency, start_node, end_node = nil, max_steps = nil) ⇒ Object 



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# File 'lib/scout/network/paths.rb', line 13

def self.dijkstra(adjacency, start_node, end_node = nil, max_steps = nil)

  return nil unless adjacency.include? start_node

  case end_node
  when String
    return nil unless adjacency.values.flatten.include? end_node
  when Array
    return nil unless (adjacency.values.flatten & end_node).any?
  end

  active = FastContainers::PriorityQueue.new(:min)
  distances = Hash.new { 1.0 / 0.0 } 
  parents = Hash.new                 

  active.push(start_node, 0)
  best = 1.0 / 0.0
  until active.empty?
    u = active.top
    distance = active.top_key
    active.pop

    distances[u] = distance
    d = distance + 1
    path = extract_path(parents, start_node, u)
    next if path.length > max_steps if max_steps 
    adjacency[u].each do |v|
      next unless d < distances[v] and d < best # we can't relax this one
      best = d if (String === end_node ? end_node == v : end_node.include?(v))
      active.push(v,d) if adjacency.include? v
      distances[v] = d


      parents[v] = u
    end    
  end

  if end_node
    end_node = end_node.select{|n| parents.keys.include? n}.first unless String === end_node
    return nil if not parents.include? end_node
    extract_path(parents, start_node, end_node)
  else
    parents
  end
end

.extract_path(parents, start_node, end_node) ⇒ Object 



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# File 'lib/scout/network/paths.rb', line 5

def self.extract_path(parents, start_node, end_node)
  path = [end_node]
  while not path.last === start_node
    path << parents[path.last]
  end
  path
end

.neighborhood(adjacency, sources, k) ⇒ Object

New: enumerate nodes within k steps of a set of sources (unweighted) Convenience wrapper over breadth_first



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# File 'lib/scout/network/paths.rb', line 173

def self.neighborhood(adjacency, sources, k)
  distances = breadth_first(adjacency, sources, k)
  distances.keys
end

.random_weighted_dijkstra(adjacency, l, start_node, end_node = nil) ⇒ Object 



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# File 'lib/scout/network/paths.rb', line 103

def self.random_weighted_dijkstra(adjacency, l, start_node, end_node = nil)
  return nil unless adjacency.include? start_node

  active = PriorityQueue.new         
  distances = Hash.new { 1.0 / 0.0 } 
  parents = Hash.new                 

  active[start_node] << 0
  best = 1.0 / 0.0
  until active.empty?
    u = active.priorities.first
    distance = active.shift
    distances[u] = distance
    next if not adjacency.include?(u) or adjacency[u].nil? or adjacency[u].empty?
    NamedArray.zip_fields(adjacency[u]).each do |v,node_dist|
      next if node_dist.nil?
      d = distance + (node_dist * (l + rand))
      next unless d < distances[v] and d < best # we can't relax this one
      active[v] << distances[v] = d
      parents[v] = u
      best = d if (String === end_node ? end_node == v : end_node.include?(v))
    end    
  end

  if end_node
    end_node = (end_node & parents.keys).first unless String === end_node
    return nil if not parents.include? end_node
    path = [end_node]
    while not path.last === start_node
      path << parents[path.last]
    end
    path
  else
    parents
  end
end

.weighted_dijkstra(adjacency, start_node, end_node = nil, threshold = nil, max_steps = nil) ⇒ Object 



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# File 'lib/scout/network/paths.rb', line 59

def self.weighted_dijkstra(adjacency, start_node, end_node = nil, threshold = nil, max_steps = nil)
  return nil unless adjacency.include? start_node

  active = FastContainers::PriorityQueue.new(:min)
  distances = Hash.new { 1.0 / 0.0 } 
  parents = Hash.new                 

  active.push(start_node, 0)
  best = 1.0 / 0.0
  found = false
  until active.empty?
    u = active.top
    distance = active.top_key
    active.pop
    distances[u] = distance
    path = extract_path(parents, start_node, u)
    next if path.length > max_steps if max_steps 
    next if not adjacency.include?(u) or (adjacency[u].nil? or adjacency[u].empty? )
    NamedArray.zip_fields(adjacency[u]).each do |v,node_dist|
      node_dist = node_dist.to_f
      next if node_dist.nil? or (threshold and node_dist > threshold)
      d = distance + node_dist
      next unless d < distances[v] and d < best # we can't relax this one
      active.push(v, d)
      distances[v] = d
      parents[v] = u
      if (String === end_node ? end_node == v : end_node.include?(v))
        best = d 
        found = true
      end
    end    
  end

  return nil unless found

  if end_node
    end_node = (end_node & parents.keys).first unless String === end_node
    return nil if not parents.include? end_node
    extract_path(parents, start_node, end_node)
  else
    parents
  end
end