Print long numbers with thousand separators.

lib/gruff/base.rb

@@ -41,6 +41,8 @@ class Base
     DEFAULT_MARGIN = 20.0
 
     DEFAULT_TARGET_WIDTH = 800
+
+    THOUSAND_SEPARATOR = ','
 
     # Blank space above the graph
     attr_accessor :top_margin
@@ -1061,17 +1063,19 @@ def increment_color
     # Return a formatted string representing a number value that should be
     # printed as a label.
     def label(value)
-      if (@spread.to_f % @marker_count.to_f == 0) || !@y_axis_increment.nil?
-        return value.to_i.to_s
-      end
-
-      if @spread > 10.0
+      label = if (@spread.to_f % @marker_count.to_f == 0) || !@y_axis_increment.nil?
+        value.to_i.to_s
+      elsif @spread > 10.0
         sprintf("%0i", value)
       elsif @spread >= 3.0
         sprintf("%0.2f", value)
       else
         value.to_s
       end
+
+      parts = label.split('.')
+      parts[0].gsub!(/(\d)(?=(\d\d\d)+(?!\d))/, "\\1#{THOUSAND_SEPARATOR}")
+      parts.join('.')
     end
 
     # Returns the height of the capital letter 'X' for the current font and

test/test_bar.rb

@@ -33,6 +33,14 @@ def test_bar_graph
     g.theme_odeo
     g.write("test/output/bar_odeo.png")
   end
+
+  def test_thousand_separators
+    g = Gruff::Bar.new(600)
+    g.title = "Formatted numbers"
+    g.marker_count = 8
+    g.data("data", [4025, 1024, 50257, 703672, 1580456])
+    g.write("test/output/bar_formatted_numbers.png")
+  end
 
   def test_bar_graph_set_colors
     g = Gruff::Bar.new