diff --git a/lib/youplot/backends/processing.rb b/lib/youplot/backends/processing.rb
new file mode 100644
index 0000000..9b7bcb2
--- /dev/null
+++ b/lib/youplot/backends/processing.rb
@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+module YouPlot
+  # plotting functions.
+  module Backends
+    module Processing
+      module_function
+
+      def count_values(arr)
+        # tally was added in Ruby 2.7
+        if Enumerable.method_defined? :tally
+          arr.tally
+        else
+          # https://github.com/marcandre/backports
+          arr.each_with_object(Hash.new(0)) { |item, res| res[item] += 1 }
+             .tap { |h| h.default = nil }
+        end
+          .sort { |a, b| a[1] <=> b[1] }
+          .reverse
+          .transpose
+      end
+    end
+  end
+end
diff --git a/lib/youplot/backends/unicode_plot_backend.rb b/lib/youplot/backends/unicode_plot_backend.rb
index 9ead9b2..16ace0b 100644
--- a/lib/youplot/backends/unicode_plot_backend.rb
+++ b/lib/youplot/backends/unicode_plot_backend.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require_relative 'processing'
 require 'unicode_plot'
 
 module YouPlot
@@ -13,7 +14,7 @@ module YouPlot
         series = data.series
         # `uplot count`
         if count
-          series = Preprocessing.count_values(series[0])
+          series = Processing.count_values(series[0])
           params.title = headers[0] if headers
         end
         if series.size == 1
diff --git a/test/youplot/backends/processing_test.rb b/test/youplot/backends/processing_test.rb
new file mode 100644
index 0000000..94275f8
--- /dev/null
+++ b/test/youplot/backends/processing_test.rb
@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+require_relative '../../test_helper'
+
+class YouPlotCommandTest < Test::Unit::TestCase
+  test :count_values do
+    @m = YouPlot::Backends::Processing
+    assert_equal([%i[a b c], [3, 2, 1]], @m.count_values(%i[a a a b b c]))
+    assert_equal([%i[c b a], [3, 2, 1]], @m.count_values(%i[a b b c c c]))
+  end
+end