enumerable_ext.rb in abstractivator-0.10.0

- old
+ new
@@ -100,6 +100,52 @@
       primary = compare.call(a, b)
       primary != 0 ? primary : (ai <=> bi)
     end
     sorted.map(&:first)
   end
+
+  def select_map(&block)
+    self.map(&block).select { |x| x }
+  end
+
+  def single
+    if size != 1
+      raise ArgumentError, "expected a single element but was: #{inspect}"
+    end
+    self.first
+  end
+
+  def unique_by(&block)
+    self.group_by(&block).map { |_, vs| vs.first }
+  end
+
+  def duplicates(&block)
+    group_by(&block)
+      .select { |_, vs| vs.size > 1 }
+      .map { |k, _| k }
+  end
+
+  # Folds over a cyclic graph. 'self' is the root node set.
+  # Each node is visited once, in an unspecified order.
+  # Node identity is determined by #object_id
+  # @param init [Object] the initial accumulator
+  # @param get_children_proc [Proc] takes a node and returns its children (or neighbors)
+  # @yieldparam acc [Object] the accumulator
+  # @yieldparam node [Object] the current node
+  # @yieldreturn [Object] the accumulator, after visiting all nodes once
+  def cyclic_fold(init, get_children_proc, &block)
+    xs = self.dup
+    seen = Set.new
+    acc = init
+    while xs.any?
+      x = xs.shift
+      if seen.include?(x.object_id)
+        next
+      else
+        seen.add(x.object_id)
+        acc = block.call(acc, x)
+        xs.concat(get_children_proc.call(x))
+      end
+    end
+    acc
+  end
 end