Adding sampling classes to implement Histograms

lib/metrics/instruments.rb

@@ -3,6 +3,9 @@
 require File.join(File.dirname(__FILE__), 'instruments', 'meter')
 require File.join(File.dirname(__FILE__), 'instruments', 'gauge')
 
+require File.join(File.dirname(__FILE__), 'statistics', 'sample')
+require File.join(File.dirname(__FILE__), 'statistics', 'uniform_sample')
+
 require 'json'
 
 module Metrics

lib/metrics/statistics/sample.rb

@@ -0,0 +1,21 @@
+module Metrics
+  module Statistics
+    class Sample
+	    def clear
+	      raise NotImplementedError
+	    end
+
+	    def size
+	      raise NotImplementedError
+      end
+
+      def update(value)
+        raise NotImplementedError
+      end
+
+      def values
+        raise NotImplementedError
+      end
+    end
+  end
+end

lib/metrics/statistics/uniform_sample.rb

@@ -0,0 +1,38 @@
+module Metrics
+  module Statistics
+    class UniformSample < Sample
+
+      def initialize(size)
+        @values = Array.new(size)
+        @count = 0
+        @size = size
+        self.clear
+      end
+
+      def clear
+        (0..@values.length-1).each do |i|
+          @values[i] = 0
+        end
+        @count = 0
+      end
+
+      def size
+        @values.length
+      end
+
+      def update(value)
+        if @count < @values.length
+          @values[@count] = value
+          @count += 1
+        else
+          index = rand(@size) % @count
+          @values[index] = value
+        end
+      end
+
+      def values
+        @values.dup
+      end
+    end
+  end
+end

spec/statistics/sample_spec.rb

@@ -0,0 +1,22 @@
+require 'spec_helper'
+
+describe Metrics::Statistics::Sample do
+  before(:each) do
+    @sample = Metrics::Statistics::Sample.new
+  end
+
+  %w( clear values size ).each do |method|
+    it "should raise a NotImplementedError for ##{method}" do
+      lambda do
+        @sample.send(method)
+      end.should raise_exception(NotImplementedError)
+    end
+  end
+
+  it "should raise a NotImplementedError for 'update'" do
+    lambda do
+      @sample.update(0)
+    end.should raise_exception(NotImplementedError)
+  end
+
+end

spec/statistics/uniform_sample_spec.rb

@@ -0,0 +1,59 @@
+require 'spec_helper'
+
+describe Metrics::Statistics::UniformSample do
+  before(:each) do
+  end
+
+  it "should have a size equal to the initialization parameter" do 
+    sample = Metrics::Statistics::UniformSample.new(100)
+    sample.size.should == 100
+
+  end
+
+  it "should allocate an array of the requested size" do
+    sample = Metrics::Statistics::UniformSample.new(100)
+    sample.values.length.should == 100
+
+    sample.values.each do |value|
+      value.should == 0
+    end
+  end
+
+  it "should update at the end of the list" do
+    sample = Metrics::Statistics::UniformSample.new(100)
+    (1..100).each do |i|
+      sample.update(i)
+    end
+
+    values = sample.values
+
+    (0..99).each do |index|
+      values[index].should == (index + 1)
+    end
+  end
+
+  it "should update a random entry in the list when it's full" do
+
+    sample = Metrics::Statistics::UniformSample.new(100)
+    sample.should_receive(:rand).with(any_args()).and_return(50)
+
+    (1..101).each do |i|
+      sample.update(i)
+    end
+
+    values = sample.values
+
+    (0..49).each do |index|
+      values[index].should == (index + 1)
+    end
+
+    values[50].should == 101
+
+    (51..99).each do |index|
+      values[index].should == (index + 1)
+    end
+
+  end
+
+
+end