Add Array#to_ranges

lib/core/facets/array/to_ranges.rb

@@ -0,0 +1,30 @@
+class Array
+
+  # Convert an array of values (which must respond to #succ) to an
+  # array of ranges.
+  #
+  #   [3,4,5,1,6,9,8].to_ranges => [1..1,3..6,8..9]
+  #
+  # CREDIT: Adapted and debugged by Ryan Duryea
+  # from https://dzone.com/articles/convert-ruby-array-ranges
+
+  def to_ranges
+    array = self.compact.uniq.sort
+    ranges = []
+    if !array.empty?
+      # Initialize the left and right endpoints of the range
+      left, right = array.first, nil
+      array.each do |obj|
+        # If the right endpoint is set and obj is not equal to right's successor
+        # then we need to create a range.
+        if right && obj != right.succ
+          ranges << Range.new(left,right)
+          left = obj
+        end
+        right = obj
+      end
+      ranges << Range.new(left,right)
+    end
+    ranges
+  end
+end

test/core/array/test_to_ranges.rb

@@ -0,0 +1,13 @@
+covers 'facets/array/to_ranges'
+
+test_case Array do
+
+  method :to_ranges do
+
+    test do
+      [3,4,5,1,6,9,8].to_ranges.assert ==  [1..1,3..6,8..9]
+    end
+
+  end
+end
+