spec/unit/test_aggregator.rb in alf-0.10.0 vs spec/unit/test_aggregator.rb in alf-0.10.1

@@ -34,10 +34,25 @@
 
     it "should behave correctly on max" do
       Aggregator.max{a}.aggregate(input).should == 3
     end
 
+    it "should behave correctly on variance" do
+      vals = input.collect{|t| t[:a]}
+      mean = vals.inject(:+) / vals.size.to_f
+      exp  = vals.collect{|v| (v - mean)**2 }.inject(:+) / vals.size.to_f
+      Aggregator.variance{a}.aggregate(input).should == exp
+    end
+
+    it "should behave correctly on stddev" do
+      vals = input.collect{|t| t[:a]}
+      mean = vals.inject(:+) / vals.size.to_f
+      exp  = vals.collect{|v| (v - mean)**2 }.inject(:+) / vals.size.to_f
+      exp  = Math.sqrt(exp)
+      Aggregator.stddev{a}.aggregate(input).should == exp
+    end
+
     it "should behave correctly on concat" do
       Aggregator.concat{a}.aggregate(input).should == "1231"
       Aggregator.concat(:between => " "){ a }.aggregate(input).should == "1 2 3 1"
       Aggregator.concat(:before => "[", :after => "]"){ a }.aggregate(input).should == "[1231]"
     end
@@ -48,10 +63,32 @@
     end
 
     it "should allow specific tuple computations" do
       Aggregator.sum{ 1.0 * a * sign }.aggregate(input).should == -3.0
     end
-    
+
+    describe Aggregator::Variance do
+      let(:values){ [1, 2, 3, 4, 5, 6] }
+      let(:stdev){ Aggregator::Variance.new }
+      specify{
+        memo = values.inject(stdev.least){|memo,val| 
+          stdev._happens(memo, val)
+        }
+        stdev.finalize(memo).should eq(17.5/6.0)
+      }
+    end
+
+    describe Aggregator::Stddev do
+      let(:values){ [2, 4, 4, 4, 5, 5, 7, 9] }
+      let(:stdev){ Aggregator::Stddev.new }
+      specify{
+        memo = values.inject(stdev.least){|memo,val| 
+          stdev._happens(memo, val)
+        }
+        stdev.finalize(memo).should eq(2.0)
+      }
+    end
+
     describe "coerce" do
      
       subject{ Aggregator.coerce(arg) }
       
       describe "from an Aggregator" do